Hi Jo,
I bought a Theraline Caesarean Belt to wear afterwards, but to be honest I found it really uncomfortable so only had it on for 5 minutes! The theory was good - you could have cushioned, warmed or cooled padding and a plastic protector - but the corners of the plastic bit were so sharp they kept on digging in each time I sat down. Without the protection of the plastic, there wasn't much point in it as the belt itself offered no support, it was just like a bumbag. I got mine from ebay, but I know mothercare sell them. They have good reviews so it looks like a lot of women found it useful!
I found cheapy jogging bottoms and high-up granny pants to be perfect - the thick waistband on the bottoms offered enough support and the granny pants were clear of the scar.
Good luck with your c-section I hope it all goes well!