Floor insulation method?

[lost in space]

JoeH wrote:
Rigid foam with an underlayment on top of it can be weight bearing, and will insulate the whole floor more evenly. Would have to check what is currently available.

Insulating underneath just between the floor joists will also work. But the joists themselves may have lower insulating value than the rigid foam.

Sleepers would have about the same insulating value as the joists.

If the T&G flooring is visible from below, a vaport barrier under an overlayment, with batts underneath between the joists and sheetrock could have a big effect, regardless of the windows. There could be a lot of air getting past the T&G.