Gestalt characters might be a good way to go for a solo to give them a fighting chance as DaveMage suggested. In this case I would go with Rogue/Cleric. The cleric can do well at fighting and healing themselves and the rogue bit will give them a little better chance at handling traps. Level wise with Gestalt I would say 2.
With no Gestalt I would start at level 3 and still do a multiclasses character. 1 level of rogue, 2 of cleric and probably a dwarf, maybe human. For many of the same reasons above.
How about a gestalt Asimir paladin sorcerer, starting at level 4? You've got healing, good saves, melee and arcane spells. The only thing this character can't do is the whole traps/locks thing. I don't know if that's a problem in WLD or not. Give the character the Battle Casting feat and he/she will be able to cast in light armor with no penalty.
I'd think you would want truly heroic ability scores though.
I would strongly recommend a character that can deal with traps. There are a LOT of them in the WLD. Depending on how you want to play it, a diplomatic character might be able to recruit helpers or at least play enemies off against each other in most parts of the dungeon.
Apart from healing, I would suggest a rogue/fighter. Magic users would seem to me to be the easiest to do without in that adventure. If you use Arcana Evolved, an akashic/ritual warrior combination might work nicely.
Maybe give the character a ring of regeneration as a family heirloom?
I like the Gestalt idea...but I suggest Dwarven Fighter/ Artificer. Instant use out of any magic items found. High survivability. With just a couple of items, the character is a potent wizard *or* cleric substitute. Plus, the character has knowledges and skills that will make them great at the WLD...and Trap Sense.
Heavy armor, good weapons, any items use, Trap Sense, Dwarf stonecunning...where can you go wrong?