Hi K.,
I don't know details of how you get along with your MIL. However, if the only issue is that you want your own family time, make it happen and then count your blessings.
Does she help you around with your son? What I mean is, is she a sit around all day long MIL or an active one who takes the time to play with her grandson?
If you are thinking of going back to work, wouldn't it be wonderful if your MIL could be there for you guys to help out with babysitting?
I don't have my mother living near me now (she moved to Nicaragua when she retired) and my father moved to Florida when he retired (with his wife). We only have my MIL who comes and goes for months at a time. When she is here, she does make herself useful and we still find our "family time". Even if just to go to the store together or play around in our bedroom with the girls, just the four of us. She very much respects that and we live in a two bedroom apartment.
So by "make it happen" I don't mean start a conflict in your marriage (because inevitably, if your husband wanted to have her mother move out, he would've been working at it already). I mean make the best of it, and enjoy the time you have.
Good luck!
M.