I admire your honesty :D How long do you think you can bear it? I mean, when you move out of the house you can do whatever you want!
OR you make a deal with your mum. You tell her that you will go to church till a certain age, and then you will decide if you want to continue the churchgoing or not. Don't ever do it just to please her though, she will keep on guilt tripping you forever. My opinion is that you can pray, serve and believe in god even without going to church every Sunday. If you stop going it doesn't mean you turn your back on him(or her :D).
I know you might feel guilty, but apparently you don't feel the need to be as devout as your mum. Your mother might not understand though, but she loves you, so in the end I think she will respect your choice :D and if not.. well, just keep the subject religion out of dinner conversations :P