You're very wise to do both sides as this is likely to avoid any inequalities due to pad material causing pulling to one side. You may also see pulling if you replaced only one side due to the fact one side - the old pads - are well bedded in - whereas the new ones will need a few miles to settle in. So, always do brakes in axle sets regardless.
Regarding the discs themselves. Look at both sides of the actual disc. Often the outer surface will look not too bad but the inner face, because it's not so protected by the wheel, will be much more worn/corroded. If this inspection doesn't show any big problems and both faces look reasonably flat, smooth and shiny with no deep scoring of grooves you're probably not needing to fit new discs however it would be wise to check the thickness of the disc against the spec for a new one. A general rule of thumb is that 2 to 3 mm of wear puts you into replacement territory. A very quick check would be to look at the outer edge of the disc and see if a significantly detectable "lip" has developed which would indicate that serious wear has taken place. Years ago discs used to last for 3 or 4 pad changes but since they eliminated asbestos from pad material discs seem to last for only about 2 sets of pads and sometimes even need to be changed at every pad change. If you decide not to change the discs then expect the bedding in period to take longer as the face of the old disc will not be perfectly flat and the new pads will need to wear to the contour.
As to where to buy? I tend to default to my local factor -
https://groupauto.co.uk/member/24736/srs-autoparts-edinburgh/ - who are generally as competitive as buying online with the massive advantage that if a wrong part is supplied, which is very rare, I can return it for the correct replacement very quickly. I'm also very impressed with Shop4parts, who advertise on our forum (and there's a forum discount available to
donated members) and would have no hesitation buying from them. They import much of their stuff directly from Italy I believe, so some of the brand names are not that well known over here - for instance "Original Birth" - but the quality seems to be very good and I've had no problems with anything they've supplied to me (I rebuilt my entire front suspension on the Panda with parts from them)
I'd be careful about buying from unproven sources as there's plenty on the internet about counterfeit and poor quality parts - Monetary cost isn't everything! Whatever you decide to do, good luck with it and do let us know how you get on - some pictures, if possible, would be nice too?
regards
Jock
