K.D.
I did both SAHM and working mom. It all depends on balance and how much socialzation you need. Its tough to stay home, its also tough to work and let someone else take care of your kids while your away.
Before you quit your job consider setting up some "activite time" just for you and your baby while mil cooks or does laundry or something. After all shes there to help you and your husband right? Also most daycares dont mention the milestones to parents so that mom & dad can think they saw it first this might be good for mil to know. Or if she just cant keep a secret maybe she can have a disposable camra to record the big event for you.
For me staying home was just exausting and lonely. Of course there are times now it seems like a paradise, but for the most part I like my job and I cant quit because my husband and I own the company (I also cant quit thinking whats next? even at 2:34 am) However when Im at home I concentrate on my kids, we read, watch an alphabet video or play silly games.
Go with what works for you and your child. Best wishes!
K.