With mine i used to put a small blanket over the grobag when we went to bed as that's when the heating went off and it began to cool down. I also dressed them in shortsleeve vest plus sleepysuit at this time of year. But I have never co-slept so can't advise for that bit!
DS goes to sleep in a ls vest and 2.5 tog gro bag. He's still in our room and during the eve the monitor shows the temp as being 21 degrees, so quite warm.
But, during the course of the night the temp will of course drop, so he might start to get cold and wake up.
And then at sometime during the night he'll become impossible to settle in his cot and will come in with me. I'm careful about not covering him with my duvet, but he gets so close to me, I must really heat him up.
Basically, what part of the night do I dress him for?
And btw, he's a TERRIBLE sleeper, so maybe if I added a layer his sleep might get better clutches at straws