My 7 month old is in a long sleeved vest and 1.5 tog gro bag. It's pretty cool in our room at the minute, def under 20 degrees but will warm up a little once our body heat starts to work. She's perfectly warm enough.
There's a chart on thevgrobag site with recommended layers. ATM my dd is in a pj top and 2.5tog. It doesn't look like it's enough compared to my big duvet but she sleeps through ok. Think she's wake if cold.
My ds was born in September 2015. The 1st winter he was a few months old, he slept in a vest and babygrow with a cellular blanket and the crib bedding set coverlet over him. Last year he was in the cot, he had a vest, babygrow or pyjamas, the cot bedding set coverlet and the cot set fleece blanket when it was really cold. This year he is in a toddler bed, with pyjamas and a toddler bed duvet over him. He's as warm as toast, he's a warm blooded child anyway, and hates being too warm. (I've never used sleeping or grow bags as I don't see the need and he'd of hated them anyway, he always kicks the covers off).
Oh thanks for the link and the answers, that’s really helpful. I don’t think he’s overheating. His head and hands and back of neck feel cool, which was why I was worried. I would be bloody freezing without my thick PJs, 2 duvets and hot water bottle!