I would do like Katie said, lighter pjs and lighter sleep sac or ditch the sleep sac, maybe leave the room cool but I'd add a blanket before the NW. I does depend on how old your LO is, where/how they sleep and if you are comfortable to add a blanket (SIDS wise younger babies are safer in the sleep sacs). Our house is drafty so the temp drops quite a bit at night and I've added a blanket (or several) since he was quite young (although prob not much under 6 months and he slept in a hammock which meant he couldn't wriggle down under a blanket anyway). TBH I've been really pleased with the early/er introduction of a blanket because he seemed to learn how to sleep with one which some LOs can find a bit tricky later on. if it is not pulled up too high and tucked under the arms it's safer.
I also used the fleece sleep suits in place of the sleep sac as it keeps arms warm and covers the whole chest up to the neck which is warmer and in the warmer weather just a regular cotton sleep suit, either way I added a blanket later on. he now has a duvet and I still go and add a blanket when I go to bed!