Looking for some advice for a gestalt lvl 19 character

[Mai]

So In our game, "Quell the Leviathan", we are currently playing gestalt level 19 characters, and our DM has said that once we level past 20, we are likely to be picking 2 more classes to level. This would make us very OP, were it not for our DM's amazing ability to create terrifying monstrosities. Our last boss fight, was against a death knight with, so far as we know, 20 levels of paladin, who oozed a miasma with various properties like antimagic, destroying magical effects, choking people, etc. In addition as he had power word kill, stun, pain, blind, etc? as legendary reactions if I recall, though the first could only be used once. And that was just after a mid boss of 2 dullahans, including their mythic forms after death, and the above death knight's simulacrum.

Anyway, my character is Faen, a level 19 gestalt way of mercy monk and mood druid. Here are her stats:
Str: 14
Dex: 18
Con: 15
Int: 14
Wis: 20
Cha: 10

We have 3 mythic boons:
Boon of the dragonsoul, allowing me to wildshape into young true dragons, the boon of combat prowess, allowing me to declare 3 misses hit per short rest, and the boon of the leviathan, allowing me to wildshape into creatures 5CR higher.

In terms of magic items I have:
Elder-Behir brass knuckles that do 1d10 bashing & 1d10 lightning damage.
An amulet that gives me Ki back, when I roll a 6 on a d6 during each round.
A dagger of venom I never use.
An orb that controls all the air in the demiplane of water.... Effectively making me a demigod of wind... but I rarely use this lest I accidently **** up and cause an apocalypse, like I nearly did while attuning to it, if I hadn't saved my int save and check to understand the interface and not loose my sanity.

I am trying to think of what to do. I have an ASI to distribute, but given we are level 19, I should distribute it into something that will benefit future classes. I am looking for advice on such classes. I could have already gotten dex to 20, but as I often fight in dragon form, it seemed less benefital.

[CTurbo]

Sorry it would bug me too much to have such a high power character that doesn't have a maxed attack stat lol so I'd take the +2 to Dex.

As far as the next 2 classes, I'd go Tempest Cleric and Diviner Wizard.

Since you can cast spells while in wildshape, I would maximize my spell options. You'll also be able to cast spells while wildshaped and invisible lol

Tempest lets you max thunder/lightning damage and also lets you knock back an enemy 10ft each time you deal lightning damage which would work great with your brass knuckles.

If you don't like Cleric, Gloom Stalker Ranger would be nice too.

[Hael]

Looking at your character, you are probably a bit light on damage (assuming you aren't doing conjure animal spam), and a bit light on skills.

I would consider Barbarian (for resistances and easy advantage). I would also consider bladesinger or warmagic, b/c its going to add alot of passive abilities to your wildshape (more damage, more AC/saves, more spell choices).

There is also the rogue option for skills and some damage.

[Damon_Tor]

A level 20 moon druid is pretty nearly unkillable as long as you can stay conscious to refresh your wild shape. A level 20 monk has great saves, which makes it very hard to knock them unconscious. It's a nice combo.

I'm going to go ahead and tell you to double down on your saves: your next 20 levels (lol) should be as a sorcerer/paladin. Invest your remaining ASIs in cha. This shores up your weakest save directly, and makes all your other saves insane. It also gets you smites, which gives you a ton of extra damage considering the quantity of spell slots at your disposal.

[Mai]

Those are some interesting suggestions. I can see the value in paladin, given our spell slots seem to stack. (Which yes, is insane) Paladin would provide a great use of said spell slots which, many of which, I can't use much of when wildshaped. (Because wild shape casting only works on spells with no material components.) Granted at our level, it will take 5 more levels to get another ASI, which means investing in cha will be hard. Any spells and features based on cha would be really weak for a while. Then again I perhaps shouldn't min max too much anyway.