I have a canoe which I don't use that much. It is light and short for a canoe but it's still bulkier than the kayak. I use that when the kids or wife want to go out. The kayak I have is a hertage featherweight 9'5" 36 lbs. I guess it would be cheaper to buy a good seat than sell it and get a float tube. I guess you don't sit much higher on the SOT type of kayak. My back dosen't always hurt only if I sit straight. If I sit at a slight angle it's a little better, not as much pain. I don't know that the float tube is the answer either. I like being dry. I'll have to work on the casting problems also.