I recommends Febi/Bilstein parts. They are great quality at a good deal.
If you are going to do that much work... since all W123 are OLD!!!... you definitely should change your spring and spring pads too.
If I were you, I'd just buy lower control arm unit and put it in. The control arm bushings on your car is cracked by now.
The rear, you will have to press those bushings out and put new one in... trailing arm I think that is what it is called.
You should also change out the sub frame bushings also... gone by now too..
New spring pads all around... new sway bar links and bushings all around too... I mean all of them including the bushings that hold the sway bar... if it is not too much work.
New shock absorbers. While you are there, change out all those rubber brake lines.
Did I miss anything else? Oh yeah, definitely get the right spring compressor... they can be rented or just buy your own for under $200 on ebay... alkyracer I think is the seller who sells great tools sold by Baum.