Cellular blankets are best for the reasons mentioned below. Each fold is another layer, so just once over baby and tucked under the mattress on all sides is best, with baby feet to foot. The Lullaby trust has good advice on layers and temperatures. A good room thermometer is the Gro Egg, but there are much cheaper ones available!
When I left hospital with DD in Oct 2013 advice was that swaddling is no longer recommended due to the risk of overheating. That said, lots of people do it because the straitjacket effect helps baby feels secure. Both my babies slept with their hands by their ears so swaddling was no good for us. DD always liked to have her feet covered - you get to know your baby's little ways.
Do remember we're having summer babies! We won't struggle to keep them warm.
I think grobags start from 10lb, but you have to be sure their head is too big to wriggle into the bag. After that they're amazing. We're moving DD I to the 18 month+ ones in the next few months. Couldn't do without them now and they're a great sleep cue too.