Upvote:4
Most hotels have "business centers" with office chairs and desks in them, though some of those do have specific hours. Many major cities also offer temporary workspaces that you can rent for a day.
If the problem is a lack of support, you might try something like this, which you can attach to whatever chair you're sitting in (I use these in the car). They should be easily packable as you could pack things between the straps and the actual support.
If the trouble is desk height (you're always slouching or bending over to see the screen), then the best you can do is get a lapdesk or build one out of books to add support.