My team suggested ultraslim shakes from Tesco for early on but as with all things WLS related, every team have their own rules so you're best checking with them. I was given a comprehensive booklet before my op detailing exactly what I could have at each stage so I had that to refer to. I also have an email address for my dietician so can contact her easily with any questions.
I too was told no pips, seeds or skin on fruit or veg for months post op and to be careful long term although I'm nearly 8 months out now and don't seem to have a problem.