Spent a bit of time looking around for an easy to run #activitypub server for a single user - I'm wholly unconvinced that Postgres is necessary for something at this scale.
Played a little with micropub.blog, but settled on @gotosocial after a relatively quick test.
Docker based setup was simple - integrated the sample docker-compose configuration into my existing setup (to leverage Traefik), some DNS wrangling and it's off and running.