If you have access, a really good sports Physio is likely the best place to start. Then depending on your diagnosis orthotics may be required short-term (some conditions) or long term for others or not at all. There is a growing movement that says orthotics are “for Christmas and not for ever” compared to previously where often people had them for life. Please don’t rely on a shoe shop’s comments.
If you are in the East Midlands, you could self refer to the University School of Podiatry at Northampton. This is a cheap, but really thorough service in my experience, although the students may scare you into thinking your legs are going to fall off, before they get their combined thoughts together.
There are a few podiatrists that posts on shoewawa that have given some great answers and is worth searching for.