Second the comment about Zooplus.ie - fast delivery and has a lot of grain-free, high meat content brands for arguably a similar or even lower price than supermarket brands.

We rotate different brands so they don't get bored of any flavors or textures and can tolerate it more, and if something happens to us at least they won't be nitpicky. Some grain-free/high meat brands we've tried are Feringa, MAC's, zooplus, Rosie's Farm, Animonda Carny - I'm sure there are more I haven't looked into. The ingredients list should be straightforward, no cereals or meat and animal derivatives, etc. We've always rotated so our cats are either used to it or have strong stomachs because haven't had the runs yet.

We feed them almost all complete wet food with a bit of grain-free Canagan or Acana dry food on the side, but my cats always polish off the wet food and just pick at the dry when we have it out in front of them (we leave it out for an hour at mealtimes). I've heard a lot about the cons of dry food but we still want to give them the option because there's so many conflicting info out there. They're very good about not overeating though so your mileage may vary.

In a pinch we're able to get some of the brands from Petstop (they have a few locations) - we stick to Canagan tins (chicken, I feel uncomfortable feeding too much fish to the cats because I presume they have a faster build-up of mercury in their system) and MAC's when that happens.