My old "fat" PS3 YLOD'd twice, didn't fix it the second time. Just buy the Slim. It's highly unlikely that you'll get the YLOD. Mine is was pretty old and I played it a lot.
YLOD is not a glitch, it is a result of either PSU failure or overheating of the motherboard, causing the CPU or GPU soldering to melt, rendering them useless. It is almost always the latter.
If you are really paranoid about YLOD here are some tips:
Do not put it down vertically. Leaving it flat generates less heat.
Keep it far from walls, In a not compact space.
Keeping it on box or something, like the one your PS3 came with, will vent the heat down.
Carpet traps heat.
After a long gaming session, leave it at the home screen for five some minutes so the PS3's fans can cool the console down.
If you get YLOD, there are some guides on youtube, chech them out.