Love the idea of additional sleeping space -- perhaps add wiring to the wall above each side (the far left-hand wall and the far right-hand wall) for a swing-arm lamp for cozy lighting ... OR add a swing-arm lamp to the far left-hand side of the left window AND to the far right-hand side of the right window ....

... And I would take the pantry cupboard right up to the top of the ceiling ....

Good idea. I'll do both teacats

The last cottage I stayed in had a custom window seat about 28"x80" and it accommodated an overnight guest and frequent maps.

That looks very odd and unsafe. If you want sleeping space, I would just put a day bed against the side wall. You may be trying to fit too much into the space.