I think the most important question is this - what kind of role are you going to be playing? We can optimize the hell out of just about any concept, but its best to have an idea that you want to aim towards. Best at weapons / melee master? There's a couple of ways to max out being a support buffer. How about a super skill monkey - mixing bard and rogue is a rather interesting twist for not only being an Expert at so much, but the Lore bard can give you even higher skill checks on top of taking Guidance.
How about a Bladesinger 18 / Eldritch Knight 20 / Paladin 2? Its a pretty fun combination, if I do say so myself. This allows using smites on top of 4 attacks (more if you haste), really high AC and Concentration saves, and the ability to cast Shield and Mirror Image (or see invisibility, depending on needs) an infinite number of times a day. Eldritch Knight brings Action Surge teleports and inflicting disadvantage on saving throws, very good abilities. War Magic is a bit tricky at this high level (you usually are too busy smacking with a sword and you're using spell slots to smite with and absorb damage), so you might prefer going Battlemaster instead of Eldritch Knight. If you do so, though, you lose out on an extra 6th and 7th spell slot, and given that you should have Foresight up and a couple other abiltiies, I feel like most maneuvers are less useful. I know you didn't want paladin, but its low enough level that it doesn't do much other than boost sword damage and give another Fighting Style.
We can look into a master archer (valor bard, arcane archer, some ranger perhaps). This gives you access to Swift Quiver as well as Foresight again.
Revised Ranger Stalker, mixed with Assassin, is actually a pretty powerful first strike, first kill option. I'm quite the fan from a brief look at it. Poison, sneak attack, hiding options, first attack letting you hit first. No matter what angle you take, mixing Shadow Monk, Stalker Ranger and Rogue make you a very good hiding style character. That's pretty exceptional.
The Sorlock is still pretty powerful option even at very high levels. If memory serves, you can get the Mephisotopheles Invocation so your eldritch blast shoots a fireball as part of the same spell, then combine that with Quicken Spell. Three spells in the same turn. You can use the Warlock spell slots to regenerate your sorcery points, then short rest to refill. Hrm... maybe aim for Empowered Evocation at wizard 10 too, so that way you get Int + Cha extra damage to fireball spells?
Speaking of Wizard and Sorcerer... Diviner, Chaos, the Lucky Feat, and Lore bard. Lots of manipulating luck and people's dice pools? Hmm... I'll have to think more on this.
Paladin-warlock is a good option, but you're already doing that elsewhere.