I have a s&w m&p 15 sport and was wanting to swap out the upper receiver for one with the dust cover and forward assist. Any ideas on which upper would work best? I was wanting to just get a stripped upper and swap everything over to the new upper but didn't know if it is worth it? Any help is greatly appreciated, thanks

Receivers are pretty much universal, though some have slightly different finishes.  If you got the know how and the tools a receiver should cost right around $100.

It is worth it if that’s the way you want it, all other reasons aside.
If I had a YHM upper that fit a S&W perfectly that does not mean your results would be the same.
There is simply too mush tolerance spread among the different manufacturers.

It can be done.

Do you want to invest in the tools required to do this properly without structural or cosmetic damage ?
Along with proper tools you will have to bring some skill which can be learned.

Once you have the tools and pull it off successfully, you will want to scratch build another one.
Then you'll think, crap, I should of just sold off that Sport as is and bought/built new.

If it were me, I'd sell the Sport as is.

OP, I did exactly what you're contemplating when I got my Sport over year ago.  Even though there is no real need for a forward assist and dust cover on most civilian ARs, I wanted both on mine for reasons of standardization (and because it doesn't seem right, to me, to not have them).

I already had the tools as well as experience swapping them out, so it was no big deal.  I used a BCM upper, which turned out to be a near-perfect match in fit and finish (for those who care about such things).  I believe you can currently get blemished uppers from them at a good discount.

I already had a use in mind for the original upper before I performed the swap.  It now has a .22 barrel and is my dedicated .22 upper.

Glad I made the swap and haven't looked back.