So, Little P still sleeps in a sleep sack at 27.5 months. The main reason is to prevent him from climbing out of the crib!

Thankfully he's small enough that I think he will fit in the XL sleep sack (the large is getting too small for him). We went from swadles to donated sleep sacks without tags (therefore I don't know the material), so I'm wondering how thick the 100% cotton Halo Sleep Sacks are. We want him to wear them in the summer nights and we keep our thermostat at 77 degrees at night, so I don't want him to overheat!

Who has the 100% cotton sleep sack and is it lightweight enough for summer? OR would we need the Muslin sleep sack? Just don't want to buy something online that doesn't work and have to return it.