I'm sure other hips and knees folk will be along with advice. You might find the dedicated 'hips and knees' thread useful and supportive, too.
It seems a bit extravagant to buy new clothes for what might only be a few weeks post op. Have you nothing suitable already? Are you thinking of this because you think that the operations site might be affected by what you wear, or for ease of dressing with a leg that does quite do what it's asked to do for a while😁
I very rarely wear skirts or dresses, I wore loose fitting trousers post op. The operation site is well covered with a dressing so it won't be irritated by loose fitting clothing.
If ease of dressing is what you had in mind I had a 'grabber' which helped a lot in pulling on trousers (and putting on knickers.. ) If you have a husband he could come in useful, too... I already had a grabber, but if you don't, you may well be given one on discharge from hospital.
My op was last August, warm weather so I went sockless for a while. By the time I needed them I could get them on by myself. If you want to wear socks you can get a nifty gadget to make putting them on easy. I'm sure the others will tell you about it.
All the best your forthcoming life changing operation