If you have persistent pain in your knees and hips, and waddle round like a duck, you need to do something about it. An NHS physio might be able to give you some exercises to do that will sort the problem by strengthening your arches, if your local trust employs any and you manage to get to see one of them. Otherwise try a private sports physio.
Only if you’re suffering very badly, or have neglected the problem for a long time, will you need custom orthotics. You can get very good ones through the NHS, if you live in the right area, but you might well need to go private. Off the shelf insoles are the next best thing if you cannot get custom orthotics and there are lots of good brands out there such as Footreviver, Nuovahealth etc..