It is as simple as a seed phrase generator, except where it’s not. You go that route and you’re going to need a way to send transactions to the network and such. I don’t believe that’s all that difficult, but I’ve never tried it and would depend on your tech skills and comfort level.

I have a hardware token, and that’s what I’d suggest. There’s the extra security of the hardware in that I can just leave it laying on my desk and it’s not internet connected or even powered up when it’s not actually in use. I have the Ledger Nano S, but it’s been years since I bought it so I have no idea the current options. I know one limitation is it can’t hold all that many coin types at once, but I really only hang on to Bitcoin and Bitcoin Cash, but I’ve had others in the past on there.