Three main choices: Subaru Genuine Coolant (Blue in Color)
Zerex Asian (Blue label Blue in Color) Very Hard to find in my area, tried all autoparts stores NAPA, Olympus, Advance etc
Peak Global Coolant (Gold Bottle Green in Color)
Since in the owners manual you can use the green stuff Peak is usually cheaper in price.
And always use the Coolant conditioner additive, it works.
Resurface your heads. You can do it yourself, find the link, it's really easy. Or call around until you find a machine shop that isn't scared to resurface the heads without doing a complete valve job. If you have no idea where to start - you can ask Subaru dealer who they use. They rarely use machine shop services, most don't resurfaces heads, but they usually have a go to shop for those few times they have an outlier issue.
You don't have to drive to a dealer - you're doing a standard headgasket job - just order the parts and have them mailed to you. for many people the online prices are 20% less and th $20+ in savings will offset shipping and make price a nonissue.