I also don't see any significant reasons not to simply upgrade your computer since that's what you're currently using and probably has the most convenient upgrade path. I also don't see any issue with staying within the Apple ecosystem, and all of the other music streaming services have Apple client applications anyway.
There are other options but it can get confusing and will require you to learn a new UI to play your music.
There are other options but it can get confusing and will require you to learn a new UI to play your music.