That stung a bit, but I get what you are saying.
Everything I say stings a bit, ignore it and look for the what I'm trying to say. Taking CL losing classes is counter productive from what seems to be the goal of this thread.
You've got one mandatory CL loss, your class you want to use.
You want Blue Mage in theme and homebrew is open.
This seems to be the bottom line. Where to go from here?
Which base class do you want to build from? Sorcerer? Wizard? Blue Mage? Duskblade? Arcane Swordsage? Another thing to consider, given the allowance for home brew, you could even ask for a Blue Magic refit to any of those classes. Wizard can handle that though already existing rules with fifteen minute breaks between battles or Sorcerer with a day or two of retraining a spell known. It's not a stretch to ask for a minor change in the time it takes them to learn a spell they seen (provided they can said level of spell of course). A Blue Mage Swordsage sounds awesome, it would go against the school limitations noted for the Arcane Swordsage but still. Any of these classes would be suitable, Monk sure isn't.
Top gish PrCs are JPM and Abjuration Champion. AC is only 5 levels and full while JPM ranges based on how you set things up. Like if you use feats for entry and exit at the 5th level it's only one CL loss, and you have the option of another CL loss for Quickening Strike as well. Other wise, it could be up to -3 CL which is very harsh. There are other gish flavored PrCs, some Eberron mount based one that doesn't give too much, a Dragonlance one for dip for -10% ASF, Core's Eldritch Knight, etc. It's just they fall short of the other two outside of specific applications.
Sublime Chord is an excellent way to have an end game caster off a melee only base but comes into play much later in the game. Like Anything 8 / Bard 1 / Arcane Weapon Master 1 / Sublime Chord 1 / Arcane Weapon Master +9. But those first eight levels really are forget able, like if they were caster based then everything it offered will be outscaled and you'll ignore it. If it was melee based, the traits will probably be used but you spent half your character's life hitting stuff and moved to casting spells after his mid-life crisis. Then levels 1~6 are spent
catching up to everyone else. So I'd skip Sublime and look else where but this is still a commonly mentioned PrC and is quite powerful by level 20.