If you get a phone with 2 sim cards you can use one only for WhatsApp and the other for everything else.
I was even able to use WhatsApp while abroad and my sim card not working for a month, it might be only needed for setting up WhatsApp once at the start and then swap the card.
You only need to be able to receive an SMS for setup - I ported my cell number to twilio long ago for spam prevention purposes, but can still use whatsapp / signal.
I was even able to use WhatsApp while abroad and my sim card not working for a month, it might be only needed for setting up WhatsApp once at the start and then swap the card.