you can find loads of review on youtube, mainly from US campers but increasingly from UK campers.
They normally buy from aliexpress
https://www.aliexpress.com/ which is a retail arm of alibaba which acts as a B2B (wholesaler), but you can also buy through ebay.
The key manufacturers are usually Naturehike and 3f UL Gear (for tents), Aegismax (for sleeping bags) but there are others and they all seem to do the same tents or bags.
They even do dyneema bags.
I've been tempted to buy, but you never know what they really weigh, what the fabrics will do, or whether the feathers are ethically sourced.
I'd suggest finding an item that you like the look of, then searching youtube for reviews of it.