This is something I struggle with.
If I used a second phone, where would I keep it? If found, how would I explain it? If I had one, would I be comfortable not deleting all the messages (even if password protected)? To be of any use when I'm active it'd need to be on my person, and I often send texts descretely (when with others). I think it'd create more problems than it solved.
I don't think there is a risk free way of doing it. I punt rarely, and I use my normal phone and number, deleting like crazy after any messages. My phone has fingerprint security, and I turn off 'homescreen' notifications, and mute notification volume. I've never had a w/g call me, and never had them text me days later. But, I know it's far from risk free.
My phone can take 2 sims, but IMO that would just complicate things and lull me into a sense of faulse security. I might investigate the apps mentioned.