Wood. Lots of warm, cozy wood. Thick seat cushions and soft places to lean while reading or relaxing. Avoid as much as is physically possible in the way of visual obstructions or head banging protrubences. Carpet feels good on the feet but attracts sand and fleas (if you have a pet) so small throw rugs help, but they MUST have sticky rubber backing or they become skateboards at the speed of light. And clean them often. Replace them a lot, too, for fun and a different look.
Insulate well beneath the deck and cabinroof. I have laminated in thin wood and rigid foam insulation. I also like thin rigid foam on the hull down to the waterline, or cabin sole. This makes the boat MUCH better at holding cool air in the summer and warm air in the winter. Exposed fiberglass areas create air circulation that is sometimes so active it feels like a draft from outside.
And one other thing - before you go about doint the interior, check all chainplates, cleats, etc, etc deck hardware and fills and on and on, and rebed/reseal EVERYTHING you possible can. 30 year old sealer was not as good as todays, and even if some of it was, it's 30 years old - retire it, and don't end up with leaks ruining your new interior.