Jodie,
You really need to get in your protein and you'll only get enough if you do protein shakes. I do mine with water no milk. I try and get in 3 30 grams each a day. You won't get enough from food. I'm not sure what post op diet you'll have but I didn't eat anything solid for at least 10 days. I'd buy a few samples of protein online, find a good quality one, and try out some flavors. Watch the artificial sugar - it can give you gas and really bad diarrea - think the sorbitols but I can't remember. The protein will also keep you from feeling too weak....
I had my surg. in 2005 and lost 130 initially and kept it off for 2-3 yrs. Hope this helps.
Deb