The battle sorcerer got shot down;
What is wrong with your DM?
It sounds like you need things crazily straightforward, so here is core only:
Fighter1/Wizard5/Eldritch Knight10/Wizard+4
BAB 15, casting as level 18 wizard.
If you can get Spellsword 1 from Complete Warrior:
Fighter 1/Wizard4/Spellsword1/Eldritch Knight 10/Wizard +4
BAB16, casting as level 18 wizard
If you can get Abjurant Champion from Complete Mage:
Fighter 1/Wizard4/Spellsword1/Abjurant Champion 5/Eldritch Knight 9
BAB 18, casting as level 18 wizard.