A fire sorc is just perfect for Meph. Cold sorcs can't hurt the vampires or cold-immune council bosses, so they have to abort from time to time.
Some suggestions to improve your fire sorc:
Get a Rising Sun amulet. Its absorb is invaluable if you have low resistances and it has +2 to fire skills as well. The councils' hydras and the vampires' meteors will actually heal you, the firewalls have no effect and only the fireballs will hurt a little. Later when you can afford it you can switch to the Tal Rasha set or just armor, belt and amulet. The complete set will give you maximum resistances while a setup involving armor, belt and ammy together with shako and Occy will need a few res charms.
You can kill Meph with nearly no risk if you apply the moat-trick. Teleport to the lower left of the level, then up without coming too near to the entrance of the room to the left until you are at the upper part of the moat. Ignore any vampires you encounter. You might have stirred up some vampires farther below, so wait 3 seconds to let them settle again and/or go back to their bosses. Go/teleport back to the lower right to the firepot, so you can barely see the stairs beyond the moat to the upper left. The stairs are the place where you will lure Meph to. If the council pack attacks you while you are standing there, go a step to the upper left (the lightning enchantment of the boss will nearly never hit you then) and kill them. Your Rising Sun amulet completely protects you from the hydras. Sometimes you get attacked by vampires. Care about them first, as they can become dangerous.
Then teleport across the moat to the upper left and lure Meph to the mentioned stairs at the moat. Running to the circle inlay on the floor and back is enough. If he gets stuck, run a little around and keep moving if he starts casting spells or if you trigger evil forces. Exception: Don't move, but teleport if he casts Blizzard. Teleport back across the moat and place your sorc next to the upper fire pot, so you can barely see him. He will try to approach instead of casting spells, but he is too stupid to run through the room left of him, so you can safely kill him e.g. with meteors.
The moat trick only works well if you have no merc, as he will stir up vampires or the council to the left or come too near to Meph which will make him cast his spells, so get him killed before you start Meph runs.