Since it sounds like you are familiar with all of the rental companies, you know that you can trust them.
If there's three people, I'd go with 2 bedrooms. Even if it's 2 and you go with your son (I'm guessing that's who Jack is), I'd probably go with 2.
Yup, Jack is my son - he'll be 9 by the time we go, but he's still pretty small. The places we're looking at have a sofa bed in the living room, if we all go to bed at the same time we'll have him out there but if we're still up he can go to sleep in the bed and one of us will sleep on the sofa.
But I'm stubborn in this regard. I'm at the point in my life where I don't want to sleep with someone I don't normally sleep with, even if it is my family. And I even go as far as try to get at least two bathrooms if I can.
I would love two bathrooms - I found a great place in NYC last month with two bathrooms and it made my girls trip so much better!!!! But London is so pricey I don't think we'll find a place like that.
It'll depend on your finances but yeah, that's my preference.
Although Kensington is nice too.