This is why you can't trust Google's price overview and Amazon not making the Renewed more prominent.
The price I saw was indeed Renewed.
Still the big issue is safe, genuine, true capacity battery. Samsung (last I checked) will only sell to authorized retailers.
There are counterfeits of decent third-party batteries and neighs packaging if it even has any is packaged to make it distinguishable unless you have to side by side.
All that said, I don't know what UK is like but in some US cell carriers with brick and mortar stores have rudimentary repairs shops. It cant hurt to ask one in your area if they would order you a genuine battery and sell it to you.
Regardless as DIY you still need adhesive backing for that exact phone which often comes with an inferior but "free" rear panel.
You could try eBay. Ask the seller if it's an original battery and to send via eBay mail so it's logged a screenshot of the battery health and decide if buying a used one is worth it for parts. You'd have extra stuff at least in the future. If they can't or are supposedly unsure. Walk away.
Amazon is an option for a renewed to swap parts but sellers rarely answer and you need to know about the battery.
The final suggestion I could give is VERY OBVIOUSLY DONT TELL ME where you live, even if by PM, only your general area and see if I can help maybe find a shop.
Again, don't provide me with any Serial Numbers, your name, address, IMEI, etc..
I'm in a very rare and exceptionally charitable mood.
Feel free to reach out here or XDA where I'm retired.