You were really brave to have that conversation. It sounds like your mum uses classic emotional blackmail to make you feel bad.
I really stuggle to stand up to my mum too, and invariably back down and let her have he own way, only occasionally I totally lose it and have a screaming fit at her, at which she goes all logical on me and makes me look like an hysterical fool (which of course I am being at that moment).
Theres something about manipulating mums that means you can never win, and you always end up feeling wrecked. I got a book recomended by someone on this forum called "Toxic Parents". Its a really good book - naturally it didnt go down well when my mum found it!!! She was pretty acid about me reading it!