The mail service's opinion doesn't count. The "permanent address" thing is complex and you have to comply with whatever each issuing agency says and realize the rules for one thing may differ from another, even among state agencies. Also be aware that the address you use for billing or official notifications usually does NOT have to be the same as the "legal" address for establishing residency, voting eligibility, tax liability, etc. So for example, a lawyers office that is designated as your legal representative may be acceptable for a driving license but not for voter registration, because you do not actually reside there.
People often end up just picking an address and assuming (correctly in 99.99% of cases) that there will never be an attempt to verify whether it is home or business or whether you ever spend even a moment there. However, with the focus on voter fraud and "Real Id" cards, this has become more chancey.
One thing you can do is obtain a US passport while you still have a valid CO address. The fixed address isn't strictly required, but it makes the process a bit easier. The passport becomes your basic "Real Id" and is considered the ultimate in identification (verified by the US gov't!). It takes you out of the realm of possibly being a fraud trying to get a fake Id and into the bone-fide citizen category.
Another technique is to rent a storage unit, since you probably will have some goods or heirlooms you want to keep anyway, plus maybe some health or financial records, etc. If you pick one that has a valid street address, you may be able to treat the address as our legal "home", even though you never actually live there. Then use a secondary address, e.g. a PMB or whatever, as your point of contact for mailed notices.
This article may help understand the nuances of domicile, residency, and "legal addresses" for various purposes.
https://www.escapees.com/establishing-domicile-for-rvers/