I’m a bit confused about what you actually want? Do you just want to update your packages, but stay on the same NixOS version? Just continue like before. Do you want to stay on your current version, but use some packages from the next version? That should also be possible if you somehow include that channel in your configuration.nix (though I don’t know how this would work in practice).
Personally, I just run with unstable though, then the releases aren’t that important.