As for Alby... It needs an account, and wants me to make a bitcoin wallet, which I do not want. :/
I'm not sure about Bitcoin integration, but Alby and nos2x are tried and tested extensions people use to login to nostr:npub12vkcxr0luzwp8e673v29eqjhrr7p9vqq8asav85swaepclllj09sylpugg
Discussion
I'm afraid those are the only options you have. Clients allowing users to enter their nsec directly is a huge security risk.
I honestly feel uneasy creating yet another account at Alby, just to have a wallet forced on me, if all i really want is to use my nsec.
Welp, time to poke the dev of the extension I use and see if they have an idea. :)
Heck... After reading the specs myself, maybe this should be my first Nostr project! ^^