Did Solomon himself actually offer sacrifices to other gods?

Yes, your assumption is reasonable given what your commentaries say, but it may not be correct. Admittedly, the biblical view of Solomon is overwhelmingly positive. He represented a Golden Age, in which the Temple of Jerusalem was finally established and God's blessings were poured on Solomon's United Kingdom. On the other hand, the text does imply that Solomon did more than simply build altars on the high places for his wives:

For Solomon became a follower of Ashtoreth the goddess of the Sidonians, and of Milcom the abhorrent idol of the Ammonites. So Solomon did what was evil in the sight of the Lord, and did not follow the Lord fully, as his father David had done. Then Solomon built a high place for Chemosh, the abhorrent idol of Moab, on the mountain that is [east of Jerusalem, and for Molech, the abhorrent idol of the sons of Ammon. He also did the same for all his foreign wives, who burned incense and sacrificed to their gods. (1 Kings 11:5-8)

The Hebrew word translated as "became a follower" here is יָלַךְ (yālaḵ), which can mean "walk, walked after, followed." It is probably best understood as "walked in the way of" here. It's conceivable that Solomon only facilitated his wives' worship, but if he actually did "walk after" or "follow" Ashtoreth, then it likely that he also visited the shrine in question. Offerings would be made by the priests, not the king. But directly participating the the sacrificial feast would not only please Solomon's wives; it would be an important signal to his political allies who had given their daughters to Solomon to seal their friendship. These nations had had other citizens living in Israel beside Solomon's wives: merchants, diplomats, etc.

Something to consider here is that although Ashtoreth/Astarte was indeed a key goddess of the Sidonians, she was very widely worshipped as the Mother goddess. Archaeologists have found evidence that the Goddess, as Asherah, was even worshiped as the wife of the God of Israel.

In a 1975 excavation at Kuntillet 'Ajrud (Horvat Teman) in the Sinai Desert, a pottery ostracon was inscribed "Berakhti et’khem l’YHVH Shomron ul’Asherato" ("I have blessed you by Yahweh of Samaria and [his] Asherah"). Beneath the words are drawings of a tree and of a cow with a calf. Nearby is a drawing of a "tree of life" flanked by two ibexes. A second reference to "YHVH and [his] Asherah" was identified in an inscription on a building wall. An similar reference has been found at Khirbet el-Qom, near Hebron, where an inscription reads "Blessed be Uriyahu by Yahweh and by his Asherah; from his enemies he saved him!"

This may help us understand better what was in Solomon's heart. The author of Kings wrote at a time when the Torah was very well known, but it is not clear if this was the case in Solomon's era. Critical scholars even doubt the first five books of the Bible could have been published or even written until considerably later. Although "ignorance of the law is no excuse," the author of Kings was certainly more aware it than Solomon was, and used Solomon's support of idolatry as a standard by which to judge all future kings or Judah and Israel.

It is also interesting to compare the account in Kings to the account in Chronicles. While Kings ends Solomon's reign with the report about his support of idolatry, this is not even mentioned in Chronicles. Instead, this account ends with a glowing description of his Golden Age, referring the reader to other works (some lost) which provide additional information:

So King Solomon became greater than all the kings of the earth in wealth and wisdom. And all the kings of the earth were seeking the presence of Solomon, to hear his wisdom which God had put in his heart. They were bringing, each of them his gift: articles of silver and gold, garments, weapons, balsam oil, horses, and mules, so much year by year... Now the rest of the acts of Solomon, from the first to the last, are they not written in the records of Nathan the prophet, in the prophecy of Ahijah the Shilonite, and in the visions of Iddo the seer concerning Jeroboam the son of Nebat? Solomon reigned in Jerusalem over all Israel for forty years. And Solomon lay down with his fathers and was buried in the city of his father David; and his son Rehoboam reigned in his place. (2 Chron. 10:22-31)

The prophecy of Ahijah the Shilohitie is apparently the source of the account in 1 Kings, which is included very near its ending of Solomon's story:

Now Ahijah had clothed himself with a new cloak; and both of them were alone in the field. Then Ahijah took hold of the new cloak which was on him and tore it into twelve pieces. And he said to Jeroboam, “Take for yourself ten pieces; for this is what the Lord, the God of Israel says: ‘Behold, I am going to tear the kingdom away from the hand of Solomon and give you ten tribes... because they have abandoned Me, and have worshiped Ashtoreth the goddess of the Sidonians, Chemosh the god of Moab, and Milcom the god of the sons of Ammon; and they have not walked in My ways, doing what is right in My sight and keeping My statutes and My ordinances, as his father David did. ...I will take you, and you shall reign over all that [t]you desire, and you shall be king over Israel. Then it shall be, that if you listen to all that I command you and walk in My ways, and do what is right in My sight by keeping My statutes and My commandments, as My servant David did, then I will be with you and build you an enduring house as I built for David, and I will give Israel to you. (1 Kings 11:29-38)

Ahijah's prophecy not only confirms that, whether or not Solomon personally offered sacrifice to Ashtoreth, he led Judah to worship her. Ironically if we read only Chronicles and not Kings, we would not even know enough to ask the question. In conclusion, Solomon probably did more than simply facilitate the worship of Ashtoreth. But either way, what he did was enough for the author of Kings to view his sin as so grievous as to divide his kingdom permanently and even bless the rebellion of Jeroboam I.