Wideband is the go to brand for all us dry suit divers with a pee valve. Wideband has a size guide and will send you a couple of samples. Ya ya, I know, you need the biggest one they make. 
Follow the size guide. Also, if you have never used these, make sure you’re shaved smooth. These things stick and stay stuck. Best bet when you want to remove is to do that in the shower as hot water and soap will help. Good luck in your condom cath adventure.
Ron