i love grobags! (and rarely buy them in store too)

0.5 tog is summer nights/day basically a sheet
1.0 tog is spring thin blanket (most recommended)
2.5 tog is a doona winter time (we use ours for most of the year)

ive only bought my kids one 0.5 tog grobags one each as ive found 1.0 the best! even in summer its gotta be hot hot hot and we really only used them as a comfort as they are so used to sleeping in them

pretty much all 0-6 month bags are zip on the side and buttons on shoulders it must be the safer option for that age (im not sure but i hate that design)

my kids have a mix of terry toweling, flannel or cotton bags and love them all
but just go by the tog in respect to what they are made of weve got terry toweling in 2.5 and 1.0
ive never found the material to be our issue
the zip down the middle is the fastest and easiest
i always just double check before bidding and ill ask about it of the pictures or description isnt clear (also double check your ebay as they might have explained the bag wrong!)
but we also only buy the SIDS grobag so thats why i dont worry about the inner or outta material

hope this helps and didnt confuse you more