I’ve used GiffGaff for a few refurbished like new iPhones the passed few years with my current year old iPhone 12 mini 5G with no problems at all.
I don’t think you even need to be a GiffGaff customer though I do have one of their SIMs in my phone as a back up with my main SIM being an EE eSIM.
Current cost for the SE 2020 on GG is £239 unlocked and the mini 12 is £319 as is the iPhone 8 at £139 in good condition. My wife has the SE2020 (my hand me down) that I bought new from Apple direct on a monthly 24 payment interest free credit when it was first launched.
I have problems using phones too because I’ve only got one working hand and why Ii use the mini versions but have found the face recognition of the iPhone 12 very helpful with no need to press the button to unlock and more so in shops using Apple Pay.
https://www.giffgaff.com/mobile-phones/refurbished?brands=apple