You don't need anything other than a B1 + the right rental agreements in place. You can have a building where one floor is residential and one floor is office space, that's perfectly normal usage.

With regards to setting up co-working spaces, there are loads of them now. So you should consider what makes you different.

I have plenty of experience working in London co-working spaces so can give good advice about what works and what doesn't if you'd like to arrange a call.