"Magic Earth" is unfortunately not FOSS, but it is "one of the few navigation apps that do without advertising and tracking." (mobilsicher.de). It includes also "Crowd Sourced Traffic".
What are you missing with the Firefish pwa?
I think it's possible to switch from Firefish to Mastodon if the account is only deactivated and not deleted, but Mastodon doesn't take over the posts when you move.
Overall, Hubzilla certainly has the most features, but Friendica (which is also my preferred software in the Fediverse) also has a lot of features and the largest reach. But it is probably not similar to Bluesky (which I don't know). Friendica's federation with Lemmy is very good and (Lemmy-) threads are displayed more clearly than in Mastodon, for example.
I don't know Bluesky, but of all the microblogging software, I think Misskey and its forks like Firefish have the most functions. For example, content can be structured well via Antennas/News-Picker: https://thefedi.wiki/firefish/user/antennas.
And you can also add accounts you don't follow to lists (which is not possible with Mastodon, for example).
There are several pages that keep curated instance lists and sort them by category. One of the criteria for inclusion is that the instance must not be too large: e.g. FediGarden and JoinFediverseWiki.
However, you should perhaps consider in advance whether Mastodon is really the right access to the Fediverse for you or rather one of the other services such as Friendica, Calckey, Pleroma, etc.
Especially if you are used to a clear structure like on Lemmy, Mastodon can be quite confusing because it is microblogging without context. The instances are connected to each other, no matter what software they are running.
The Jointhefediverse.net can help you get started.
"Magic Earth" is unfortunately not FOSS, but it is "one of the few navigation apps that do without advertising and tracking." (mobilsicher.de). It includes also "Crowd Sourced Traffic".