I stick to brands with TOG ratings only so I know what to dress DD in, according to the recommendations for the TOG rating.

I have some Grobags which I've bought on sale so a fair bit cheaper. I also have Living Textile bags which are gorgeous and well priced brand new (see their site) as are Dream Bags. They are my 3 faves.

As for the zips, the position is generally for different sizes to make it harder for those LO's who have worked out zippers The side ones are good if your LO is a tummy sleeper too as they're not laying on the zipper. That said, my DD has never been bothered by the zipper position.

As for materials, I find mine are all very, very similar inside and out and I think this comes down to the fact that they have TOG ratings. I'm personally not comfortable with fleece bags or any other materials that are a bit suss, may not breathe well. That's why I stick to those with the ratings.

HTH a little.