Model Release

[chil]

Hi everyone, I'm hoping that I am posting in the correct forum. I have started a business designing and printing t-shirts and have approached an Olympic gymnast about using his image in one of my designs. The image will be turned into a silhouette but will still be recognisable as him. He has asked if he would get a percentage and have imput into future designs with which I have said yes to. My question is, what type of contract do I need to get drawn up and do I need to see a solicitor to do it? My worry is that it will cost me a lot of money if I need a solicitor to do it, which I don't have at the moment. I won't go through with the partnership without a contract but just wondered what help I could get to write one? Thanks in advance.