OP can use miles to upgrade if no status. There’s an older thread about splitting the upgrade method between an MVP instant and GGU/miles for the companion. Should work the same for a GGU and miles. Since both pax will need to be upgraded together, find U space for two, choose Miles as the upgrade method in the advanced search, purchase, and call Reservations to apply Miles and the GGU.

Will need 45,000 miles for 3 upgrades, so if the OP has to purchase that entire amount, particularly if there isn’t a sale bonus, should probably look at cash fares for comparison and tossing the companion code or just go in coach.