Just off the top of my head, I'd say it's going to be extremely hard to play a sorcerer based mindflayer. Your abilities, especially mindblast and charm monster will always be useful but they will be about all you will ever be able to do because your sorcerer caster level will always be so far below party level. At 15th level when the cleric in your party is casting 8th spells of doom, you, with ECL +8-+10 will be capable of web and glitterdust (and the mindblast and other mindflayer abilities you've always had). At the +18 that the new WotC YOU-MUST-NOT-PLAY-MONSTER-PC dragon magazine has, you can't do anything at all.
If you want to have mindflayer powers and be a sorcerer, and if I were DM, I'd let you because your caster level is going to be such that your sorcerer abilities are always going to be somewhat of a side show. Even if your ECL is only +5.
But if you want to play a character with the illithid mindset, apperance, outlook, and can handle not having the abilities (just say your abilities lie along different paths), then here is what I'd recommend.
Illithid, the PC race
ECL +1
AC: +3 Natural (ECL +0.6)
Attacks: As a humanoid, not proficient with using tentacles in combat.
Int +4, Wis +2, Cha +2 (ECL +0.4)
Special Attacks: None
Special Qualities: Telepathy, Darkvision 60' (ECL +0.2)
Character class determines hid die, saves, skills, and feats.
They have an affinity for consuming the brain and brain fluid of other creatures, they just never really got so good they could hold something with the strength of their tentacles and then force their beak through it's skull. These have to find more "conventional" ways to get at a creatures brain. You can't levitate, planeshift, mindblast, etc. because you were busy learning to cast spells. Of course, that's hardly common knowledge.
I'd allow this as well in my game because the first alternative (while not unbalancing) would probably tend to be no fun), the second is not any more powerful than an aasimar or bullywug.
Just offering ideas. Feel free to throw it out the window.