There's the job guide/thread
here. A guide on BGWiki
here guide on Youtube
here and so on.
The quick summary, of course, is that bubbles are similar to BRD buffs in that they key off of the combination of two skills - in this case, Geomancy and Handbell. Effects cap at 900 combined skill, which is why you see that thrown around.
The vast majority of relevant gear there is simply the job-specific stuff, though Incanter's Torque also stands out as a very useful item.
Additionally, like BRD and COR, bubbles have gear that directly enhances them. +Geomancy adds to the effect per point. It's pretty simple though, there are two +5 Geomancy bells (Nepote Bell or Dunna) or Idris has +10.
The other thing to usually look at is Indi- duration.
More or less, just target the job specific gear and Incanter's torque. Offhand, particularly, AF hands, Relic body + legs, and Empyrean Feet (basically, some skill/Indi- duration items and enhanced Bolster duration). There are other good pieces, but those are (I think?) the ones most directly relevant for buffing.
Don't worry too much about not hitting 900 skill off the bat. A
major component of that (and why people fussing about it for Job Point parties are kinda being silly) is that Gifts make hitting 900 skill dirt simple. Geomancy and Handbell are C ranked skills, capping at 373 for a fresh 99. Obviously, merits add another 16 each, and then Gifts total a further 36 points in each (granted, the last relevant one being at 1710JP). Still, at that point, you can be at 425 skill in each,
naked. Assuming you have a Dunna for 18 Handbell more, and that leaves only 32 skill to make up, which any number of combinations of gear you'd want to use anyway will hit/break it.
So, more or less, that 900 skill goal becomes practically a given with Gifts, so you're better off just getting out there and CP'ing than worrying about hitting it immediately when you ding 99.
There are -many- other sets you'd probably want to build though - Pet regen or damage taken helps a good bit. All the normal enfeebling, curing, nuking, dark spell, etc sets. Conserve MP to stuff in spare slots (Geo- spells are very high cost), DT sets for you since you may be standing in range, and so on.