Dungeon Magazine issue 213 had a conversion of Tomb of Horrors to D&D Next (the 5e playtest rules) done by Chris Perkins. You might want to check that out if you can't wait for Tales from the Yawning Portal. (It treats poison traps with varying amounts of poison damage.)
POTENTIAL SPOILERS AHEAD!
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I DM'd a 5e party through this about a year ago and it was okay. Some of the updated material was an improvement from the original and made certain areas more fun to play (room #2, for example). I kept some of the original ToH's lethal traps in it tho, because I also found some of the watered down areas did not do justice to the Tomb's reputation (the "Agitated Chamber", for example). I used the demilich stats from the 5e MM, including the additional "Trap Soul" ability in the Acererak sidebar, but modified it to be as deadly as the original Acererak (one target, no save).
Needless to say, nobody survived. The party did make it to the Acererak's true tomb, but by this point they were reduced to three characters and were thoroughly depleted. They were no match. Even if I hadn't modified the demilich, it just toyed with the party until they were all dead. Fortunately for my players, we played this as a one-off game with different characters from our main campaign. It was a lot of fun regardless.
@Sands999: If I were you, I'd rule that players cannot choose the Dungeon Delver feat for their character for this module. One of my players did and, honestly, it really takes some of the fun out of playing the Tomb of Horrors. Save yourself the headache and just veto it.