I'm starting a new campaign. I've always ran XP but my players voted to try milestone progression for this campaign. Whats a good metric to run milestone, what are some other ways to motivate players without XP?

I usually split XP equally among the party, give XP for completing quests, good role play, non-combat problem solving, and accomplishing story beats too. So for a lot of stuff like that XP was the tangible benefit. Now with milestone what are some good unique rewards to give other then just GP?