Definitely Clarks to big in with for his first pair. They do six weeks guaranty service, ie if your little one's feet growing fast and the shoes ghey fitted become too small within six weeks, they offer free replacement.
I use TK max a lot for treasure hunt my son's shoes once I know the right size. Just randomly going there to see if I can find the next size up for the right season. Have bought brilliant bargain designers £10-£25 for a pair retail for £50-£150!. I still go back to Clarks after a couple of seasons for up to date measurement. I do buy their shoes after the fitting of course.