Hi Ryn,
Sorry, I may have missed this, but have you ruled out co-sleeping? Just that this will regulate body temperature and eliminate being cold as a problem.
Also, it is not recommended to leave babies in their capsules or carseats when they're not actually going anywhere in the car. I know that I will leave DS sleeping from time to time if we get home and he's fallen asleep, but he's a bit older now and his chest cavity is more mature. The reasoning is that the angle that the seat puts the baby's middle in compromises their breathing. It was a recent study that suggested this. I know, they can be at their most peaceful when sleeping in the carseat! However, DS has never stayed asleep when trying to move him in the carseat, but he HAS stayed asleep after getting him out of it and into the house and into bed.
None of this probably helps - sorry!