easiest would be to sign up with a texting service online that's 3rd-party in your country, get a temp number and register that for Whatsapp. Not great since you'd be marshaling two phone numbers, but fairly transparent after you set it up and they'd just see that online number, but of course would get confusing when texting friends or family on there.

hmm. I think for Europe (I mostly know of US ones) you could try Telfon: mytelfon.com - interesting they use Twilio as the backend for VOIP, so you're kind of paying for two things in one. TextNow and a lot of the US ones don't really tell you the backend bits lol.