Sleepsuit instead of sleeping bag

I am sure this topic has probably been done over and over again, but looking for some guidance.
Up until now during winter , my daughter has been sleeping in a 2.5 TOG sleeping bag, with an all in one (with feet), and a pyjama top which is I think as per the guide that comes with the Grobag for an 18 degree room.
We make sure we keep her room between 18 and 20 degrees and she seems to be happy with that.
I have recently purchased a Mothercare sleepsuit for her, which is 2.5TOG (I think!! I threw away the tag but seem to remember looking at it in the shop and thinking it was the same TOG as her bag).
I am not sure what to dress her in under the sleepsuit, mainly because the sleep suit has long sleeves, and her bag doesn't. Also as the sleep suit is obviously more fitted than the bag, I am not sure if it would be warmer simply because of this.
Does anyone dress their babies in 2.5TOG sleepsuits for bed, and if so, what does your baby wear under it?
Thanks.

DD wears a 2.5 tog snugtime one, she wears her normal pj's or wondersuit under hers, then shes under a sheet and doona in a bed (she still needs teh suit as she ends up out of the doona during the night)

Dd wears a babykids 2.5 tog one, she wears a long-sleeved all in one plus a short sleeved suit plus singleton under hers and has a cpl of light blankies over her. We keep the heater at 15 degrees over night. She seems comfy, definitely not too warm.

Oh dear, I think I am overcooking my chicken! lol. I have DS in a bonds sleeveless grow bag, he wears bonds wondersuit under that and a sleevless suit under that. No blankies as I keep the bedroom temp around 22 degrees.........I used to put blankies over him but I think he was too hot :o When we were in China I used to put him in a short sleeve suit under his wondersuit and then the gro bag and an extra couple of blankies on top too. It was pretty cold there! I'm not sure what I would put on DS if his grow bag thingie had long sleeves though, probably a wondersuit again...

My kids have the snugtime blanket sleeper with long sleeve onesie and an oil heater that comes on around 12midnight to 4am to keep them snug.