I keep pasta water in the fridge if I know I'm going to cook pasta again in a day or two.
Using less water also helps.
Otherwise, I think potato starch is the best in giving texture and thickness, but you should make sure it doesn't clump.
You can also make a water based roux and add it to the sauce. Very similar effect.
And by the way, does anybody else find starchy pasta water to be really tasty? (if it's not overly salty)