I mix my orders up with A Di Maria and my local supplier.
Before Xmas I ordered from my local Italian wholesalers Amato as I am ok to make a collection there. Going off their recommendation on flour so at the moment I am using Mulino Naldoni Sofia Type 00 Flour.
https://www.molinonaldoni.it/en/flour/pizza-sofia/25-kg which was £15.99 for a 25KG sack.
I get your point about the convenience of Amazon and what I would say is that they are really competitive on good quality DOP tomatoes. Of course you can go with local tinned from your supermarket but if you want an authentic taste then DOP is the way to go, but it does cost more.
A Di Maria, i find are quite good and usually I would get a couple of different bags of flour, then I add in my month's worth of Fior Di Latte Mozzarella. Think I paid £12.00 for a 2KG Sack. Ok it's pretty big but you can freeze it into the portion sizes you need so a bit of this and a bit of that, A Di Maria is not to bad.
Another company I can recommend is
https://www.delicatezza.co.uk/. Very similar set up to A Di Maria. The main benefit of these guys are postage is a little lower at £6.00. More importantly their range of Italian Sausage's and Sausage Mince is really good. I can highly recommend their Sicillian Sausage mince with Fennel. That cooked with some finely sliced shallots in garlic, WOW that is good.
From my point of view, I cook around 8 to 10 Pizzas a week for friends, neighbours and family so 25KG sacks makes it a bit more worthwhile for me. Once i've done with this industry, I will be opening up a Pizzeria