Honestly, if you don’t want a separate device, I’d sign up for a VoIP number. I use voip.ms, it’s a dollar or two a month for the number, and you pay per minute and per text (about a penny each, IIRC). You can forward calls to your primary number, or set up a SIP app (I’m using one called ZoiPer). I usually load it up with $20 per year or so.

And won’t survive things like… getting sprayed with water.