2015 IMac needs a new backup drive

After a great long run my 2TB external drive (Seagate) won’t mount. I’m thinking I need to replace it. Looking at Crucial X9 pro and will have to use an Anker adapter USB A to C. I’m dreading this. There are always pitfalls. My Mac is fine but looking to replace early next year so I need to back up. I’m at about .6 TB of 2 TB available and have a lot of very old files from prior migrations (I’ve always just used Time Machine). What should I be looking out for in terms of problems? I don’t think I can do cloud (except pics and music) because it will take forever to transfer? Plus my isp might make trouble. Anyway, youngsters, I started using Apple computers with the first 512k machine and the tech has gotten beyond me! Any good suggestions explain it like I’m your grandma! TIA.