I don't even know if there is an alternative to Postman. Postman is one of the "de facto" standars that I don't even waste my time thinking in another option.
In the last version, Postman got a bit more complicated, complex, than the previous versions. I really miss the simplicity of the previous version, but well... still a super nice UI.
While I'm also a big fan of Postman, after one of the bigger updates it began to start up really slow. For this reason i tried Insomnia. The former is more versatile in my opinion but if you miss the simplicity of it, maybe you should give the latter a go.
Had never heard of Insomnia, but will give it a try! Thank you!