E36 brake disks advice

Hi there.
Just a quick couple of questions for you knowledgeable lot that I would
apprecate answers to...

I have been told by the mechanics that my front disks are showing early
signs of slight warping and that would probably need to be replaced soon.
So, being a resident of the rip-off island, I am looking at the local
mechanics charging several limbs for pattern parts. I thought I'd be clever
and try to source the parts myself.
The car in question is a 1996 318ti compact(E36), not really worth spending
too much on and definitelly not driven agressively enough to warrant a
"grooved" or "drilled" disks...

Q1) The car has stock solid disks (12mm, I think). Now would I be able to
replace these with "vented" (22mm, I think) disks without having to get the
bigger calipers too?

Q2) Who makes the original disks for BMW? In other words, what is a good
make of disks to be aiming for?

Q3) Anyone able to suggest a good online parts supplier in the UK?

Thanks in advance.