i know this may not be ideal but have you thought of having an iud (the coil)? it is nearly as effective as sterilisation and last 5-10 years depending on which one you have. you can then get it replaced straightaway if you choose.
i have one in and it's absolutely brilliant! i am 22 and had 3 pregnancies in under 3 years. i have a 26 month old daughter a 16 month old son and lost my second daughter at 21 weeks pregnant back in september so i would of had 3 under 3
like you, i decided i didn't want anymore kids and my husband was due to get a vasectomy. we have now split up and i realised that things can change in your life and what you want now may not be applicable in a few years time.
please think of the coil. it is just as good as sterilisation but if you change your mind it can be removed and your fertility returns to normal. there are
so many stories of women getting sterilised and regretting it.
good luck whatever you decide