It'll probably help if you name the two countries

I have a prepaid e-sim that I use for my second country phone number. I had to put 5 euros on it and pay 5 euros extra or something, and after that I only pay when I use up the money. Only disadvantage is you have to use it once every two months or they deactivate it.

Since this would be the phone number that you'd rely upon to have continued access to those government services, I wouldn't skimp on the expense: consider the monthly charge for a domestic phone plan as a cost of citizenship or residency.

Supposing you find and set up an eSIM with a domestic carrier in that country, then one which supports WiFi calling would allow you to receive SMS/MMS from anywhere, provided that your phone also supports WiFi connectivity.

As an aside, WiFi connectivity was greatly useful when I was traveling in Japan, since I'd be back at the hotel with WiFi in the evening, which conveniently overlapped with USA West Coast time, so calls were perfectly natural.

The countries in question can vary the process greatly.

I live in a country where I pay my monthly charge for my sim, and I hold a number in another country where if you have a positive balance on a prepaid number, even if it’s not connected, it stays active.

I also believe so long as it’s connected (even via roaming) most countries won’t shut it off.

I have used Voip.ms to park my number in Canada while I lived abroad. I could still receive text messages most of the time. If not, the back up “receive a phone call” option would work.

I saw an advertisement on tv for Saily. It might be useful to you?

Is Google Voice an option?