Advice sought (but not necessarily followed)

I am planning to walk to Walsingham from my front door, because the vast majority of the way is along the newly completed Norfolk Coast Path, turn inland at Wells-next-the-Sea. Not all in one go, either - a day here and a day there, depending on public transport and time without children. 12 miles or so a day, very rarely two consecutive days.

The trouble is footwear. I've never had a pair of dedicated walking boots or shoes that have really fitted or been comfortable, and I have extraordinarily wide feet. For everyday purposes, I wear a G width, but that is only just a passable fit. Last time I had them measured the size chart gave up and refused to admit my feet were possible.

It's going to be flat - this is Norfolk, and a lot of it is along the beach.

Should I stick with the casual boots I favour from the children's section of Clarks? They don't have amazing amounts of grip on the soles, but I'm not planning to climb any mountains or parade through bogs, and they do leave me with comfortable feet after a full day of errands hither and thither on city-centre tarmac.

Are there any wider-fitting brands of proper walking boots or shoes that don't cost an eye-watering amount?

Should I just buy trainers?