when my
DS was in his sleeping bag & that was up til round 16months (so not sure this will help)...but I would put him in the bonds suits. Not the warm ones, the ones with stripes & funky patterns etc with no feet in them. That way arms were always covered & legs, feet out for comfort...then the sleeping bag as the comfort of a rug & that worked for us. This way I was ok with leaving his fan on also....we lived in remote WA & it was HOT!!
Even now at 2.5 as he never keeps under covers I still like to keep his arms covered, so I use just plain long sleeve tops, just whatever I can find & don't use a singlet underneath. I got some really nice plain coloured thin ones just a couple weeks ago at cotton on for kids.