Trying to keep baby warm while sleeping by himself

So my little guy is almost a week old and I’ve been trying to get him to sleep in our bassinet next to our bed. I know it’s a lot to ask a little guy who is used to being snuggled in my womb. He sleeps great when on someone, and has been wrapped up and in a swing for the last 30 mins no problem (I have a toddler to tend too as well).

I feel like he gets cold super easy, and that is why he won’t sleep on his own. I live in SoCal, so our winters aren’t what most would consider cold (low 50s in the mornings). He is put to bed with a hat, socks, pants and a long sleeve onesie, all swaddled together. I feel like a fleece sleeper might help more but he is far too small for newborn sizes and is too long for preemie sizes (born 6 even, is currently 5 lbs 12.5 oz). We keep our house temp set to 74, but if the heater isn’t constantly on it can get chilly (I was shivering last night with a blanket on). Any tips to keep baby warmer at night?