You might try 5m, which has worked for me, and then get a pair of neoprene socks, to give you more versatility. You have to make sure that you have a bit of extra room in your booties, for the sock to fit. Good Luck
Check with Northwest River Supplies. They have a large selection of river booties that work well. I like the Attack bootie. They are also available locally at most sporting goods stores to save shipping.
That's what I used to do . . a neoprene sock (preferably lined with some kind of soft fleece-like material) inside the booties. that seemed to work quite well although in the salt ponds in Jan or when wading through 20 feet of broken ice to get rides it was usually just a matter of time before your toes would hit the numb stage anyway. A dry suit with integrated booties would be nice!!