You know pre-paid burner phones are a reasonable option to harden security at your own pace, right?
No one is forcing you to use the same number for everything. And don't complain that it's just too expensive and unrealistic to maintain more than one phone number, because that is simply untrue.
Yes, I am aware of NIST's guidelines, regarding SMS as a layer of multi-factor authentication [0]. Those guidelines are for large organizations that dictate user behavior in a top-down hierarchy. Individual security profiles are much more flexible, and don't require the same degree of adherence to recommended practices.