If you are hosting the dinner we would suggest 2 outfits: one to cook in and one to sit down for dinner. You should look nice but be comfortable while cooking. Tight or constrictive clothing doesn't do anyone any good in a hot kitchen. Sweats are probably not a good idea because everyone gathers in the kitchen and wants to visit the cook! But no one wants to sit down to a beautiful dinner that took 3 days to cook with potato and gravy spots down the front of their shirt!
For the cook:

This plus size velour jog set is comfortable and loose so you can move around without any trouble. The jacket zips open so if it gets a little hot with the oven on you can open it or take it off. The boot cut pant and yoke jacket make it a little dressier than a sweat suit and it's just as comfortable.

If velour isn't your thing try a cute plus size cotton fleece foil print hoodie pant set. It's loose and breezy with a zip front and pockets. Great for layering so you can peal it off and the foil print is really fetching!For Dinner:
Break out the big guns and wear a plus size dress! I know you are thinking effort... but really it's a lot less work than pants and a top. Plus size sweater dresses are comfy and very flattering for all shapes. Throw it on with a necklace and boots and you are good to go! You don't even need pantyhose if you don't feel inclined.
Not feeling a dress? Try a plus size crochet trim tunic. In addition to being adorable it comes with a free pair of leggings! Simple, comfortable, breathable... can't go wrong with all of that! Put in some chunky earrings, some kitten heels and rock it out!