Hi Mark
Have you had any advice from your consultant as to when you should start using the pump. You should have probably been given Viagra or similar to get the blood flowing into the penis. I was told to wait at least six weeks before using a pump, depending on my recovery.
A medical grade pump, such as SOMAerect, often prescribed by the NHS, is the best. But to start with a cheap one from an online sex shop should do the trick. I have done a survey on pumps which you can find at the following link on this site:
https://community.prostatecanceruk.org/posts/t28948-Re-establishing-Sex-Life
Happy to give you more help if needed.