Upvote:5
As a British citizen, you can spend up to 90 days per visit on the visa waiver program (VWP). Once you have entered the US under the VWP, there is effectively no way to extend your visit. (The exceptions are for close family members of US citizens and for things like medical emergencies.)
In order to spend more than 90 days in the US, you can apply before you travel for a B-2 visa. B-2 visitors are generally admitted for six months per visit.
More information is available on the Tourism and Visitor pages of the US diplomatic mission to the UK.
You ask
Is it easy to get a visa for this?
For some people, it is quite easy, and for others, it is quite difficult. Most British citizens who can afford to own property in Florida will probably not have much trouble with it, but there are all sorts of factors that could make it very difficult indeed.