maybe put him im two sleepsuits? or two vests, one long sleeved. all supermarkets do simple cotton ones. you can also use socks as mittens. just make sure he's not getting too warm (check his neck). have you got sleeping bags? they are nice and cosy.
My 7mo is waking regularly around 3-4 am and I am now wondering if it's due to the cold - it does get pretty freezing in our room where the cot is.
She has a 2.5 tog duvet and sleeps in a vest plus sleepsuit but I am struggling to find a nice warm sleepsuit that covers the hands. The only one I have is from Gap and that one doesn't have any feet plus they cost a fortune.