Many who are on SS retirement stay unmarried for just that reason.

Nothing complicated.

You can keep separate account for separate expenses but have one joint account that you can each deposit money into for routine bills that you pay together.

Guardianship doesn't apply.

Wills are a good idea if you want to leave something to each other.

Powers of attorney not a good idea unless it's just effective only for medical and financial decisions should either of you become incapacitated.

DO NOT own a house jointly. DO NOT own cars jointly. DO NOT have joint credit cards. DO NOT have any joint debts for anything.

Because if you ever do split up (the odds are way in favor of that) you will go through living hell determining who owes what and who gets what. If you don't believe me just read these legal websites for a few weeks and see what happens to all the others who were "in love and, oh, that can never happen to us." Yet it sure as shoot did happen.