Need help! Quite a strange question...?

A good friend of my boyfriend and I is getting married to his partner Emma. They have a child who is two however he is Emma's from a previous relationship. Sadly Emma and her doctor dont think that she'll be able to have any more children which really upsets both of them as they're desperate to have a child together after they're married. What makes things worse is her eggs, ovaries and fallopian tubes are in perfect working order, its just her womb thats damaged. Thats where I come in and need your advice. My boyfriend and I definitely don't want children but I guess I wouldn't mind being pregnant as it must be pretty magical to create and carry a baby so I am wondering whether to tell my friend that I will be a surrogate mother for them after they are married. Any of you have any experience with this as I don't want to have the baby only to realise that I do want children and find it hard to give the baby up. Also just wondering how well do 22 year old bodies snap back after pregnancy considering I'm 5ft 6 and have been about eight stone for the past 5 years or so...