Look into cheap pre-paid providers. I’m in an similar situation, but with a Canadian number. I ended up on a second tier provider that charges $99/yr for unlimited talk/text (in Canada) and no data. Roaming works and I can receive SMS texts for free. I have it as an eSim in my iPhone and then have a regular Spanish provider in the sim slot for data and whatnot. I don’t actually make or receive calls on my Canadian number, though. I more or less use it receive 2fa texts and to “hold” my number. I used to pay $15/mo to have my account suspended and without any service (but “holding” my number), so this method is much cheaper.

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.)

+1 to suggestion of VoIP type service. Also look at Callcentric and voip.ms (which are traditional sip based providers) as well as others such as Skype (which does offer a pstn number option) and google voice (even though the parent post didn’t like it)

I switched to voip.ms as part of divesting myself of Google services. The webui isn't very slick but it's dirt cheap, has more features than I'll ever use, and has been reliable aside from briefly when they were being ddosed. It's also easy to add new numbers, if I decide I want a number local to somewhere else too.

The one issue I've had with it is that it doesn't accept large images (where large starts somewhere smaller than many modern phone pictures) over mms. I never really use sms/mms so I don't much care but it could be a potential problem.

I used Tmobile while living internationally for 3 years and it worked like a charm. Data was slow but was enough for things like Google maps.

If you give in and get a UK sim, you could look into ‘parking’ your number. Some carriers offer this service. There are also some third-party ‘park your number’ services though I haven’t used them myself.

"Your calls and text will not be impacted." - only roaming. So it looks like you won't lose your number. Can you enable voice mail to not miss messages, or setup a forward for calls?

If vonage operates in the UK they might be an option for a us virtual number. We use that in Canada for example.

www.DIDww.com offers numbers which can receive SMS to email, and can port your number into their service (and back out again later).