I use a US voip provider (line2) which I ported my number over to. I tried briefly to use Google Voice and it was too much of a pain to deal with; less expensive but too many pieces, including a few third-party tools and SIP providers, that were poorly supported. If you already have your whatsapp/signal apps set up to use your US number then you should be able to continue, but should be prepared to re-validate if you need to replace your phone for some reason.

For a little more than $15/mo I am maintaining my US number, can answer annoying SMS 2fa from some US services and account I still hold on to, etc. They were not the cheapest option, but when I set things up I needed to also handle multiple numbers and extensions for business purposes and so far they have been pretty good at handling the basics of what I needed. For me, the benefit of having a service that just worked and I did not need to think about was worth the cost.

(And FWIW I am on a UK esim via EE and am having no problems getting my US calls and text messages through this setup and it is also easy for me to make outgoing calls to US numbers as needed.)