Hi
From a fellow cosleeper, I feel for you. Our son (15 mo) has never been a great sleeper and if we get 4 hours staight it's like Christmas. But one thing you said did capture my attention. Why isn't he going outside?
There is nothing wrong with cold weather and kids can run and play outside when it's cold just as well as they can when it's warm. I think it just helps to dress them smart...as in what's going to give them the most warmth without the bulk which makes them feel claustrophobic and restricted. (this is important to us as we ride horses all year and he's been coming to the barn in 18 degree weather since he was 3 months old)
www.novanatural.com sells 100% wool footed union suits. Toss one on under a cozy sweater and pants and your child will be toasty, not sweaty, not over loaded with bulky coats, and perfectly warm for outdoor play. Our son wears his under his clothes in the dead of winter and when I try to put a coat ontop of it all, he pulls it off. They're the best.
Also, cold air is SO HEALTHY for kids because it boosts up the immune sysytem and helps cicrulation. Our pediatrician actually suggests sleeping with the windows open at night so baby gets as much fresh cold air as possible. Also, outdoor exercise is mentally and physically stimulating so it might exhaust him in a healthy way and promotes sleep.
As for the water issue, I don't know what to tell you. We've done everything we can think of to get our child to sleep and we still don't have any answers. But I ALWAYS notice a huge difference in the hours on days when he is outdoors for the long periods of time.
Good luck.