I do always sleep better when it is not so hot through the night and early morning,though this year,I am still waiting for the cool to arrive!!! It IS definitely darker for a half hour longer in the mornings now though,so that's nice!
It's getting warmer here but I don't think the temperature makes any difference. Light mornings earlier and increasingly loud spring dawn chorus on the other hand............ well, sleep can seem like a myth some mornings!
Yes, I love having a sleep-in during colder weather. Am nice & 'toastie' under doona!
Cat usually manages to crawl underneath it as well, & I then have a warm 'fur coat' next to my feet!