If you are moving from one UK manufactured good to another (most own brands are), the impact is negligible so I would not worry too much.
Also as others have mentioned, you don't have to be perfect. If you already own iPhones etc you don't have to ditch them as it's already a sunk cost. When they break then that's the time to make that decision. If you have streaming services, go down to one and switch around rather than having all of them. Use other search engines like duck duck go whenever you can. These small things do matter, even if all it means is that we feel better about ourselves and our local small businesses sell a few more items. Rome wasn't built in a day.
With regards to Mumsnet, you don't need to boycott but perhaps with this thread, Mumsnet might think about swapping providers, there are alternatives. Many are still US but a few are less awful than Amazon.
For all those 'whataboutery' posters, you don't have to join in, no one is forcing you. But making out that some how these Amazon jobs are worth saving instead of creating jobs in independent or domestic chain shops is frankly bizarre.
And Amazon are often not the cheapest. They rely on us to no longer bothering to check prices and opt for convenience instead. There are alternative for books too, second hand online, charity, The works and of course libraries!
And if course once again, you don't have to be perfect or do loads or in fact anything! But I would appreciate if you are in the latter group, can you start your own thread! 😂