I also have the Avent Isis Manual and its fine for my needs, but I only really express if I feel like I'm going to explode or I'm dripping everywhere. My SIL has an expensive electric double pump which I've been told I can borrow if I need to pump more often. I didn't buy the manual one until after I'd had the baby as I didn't know if I'd need it or not - I'd suggest waiting until you know what your needs are.

I also have a stereliser, the Avent Microwave one, and I do use it for the breast pump and bottles just in case. It take a minute to chuck everything in so its not any more work for piece of mind.