Need advice on replacing carpet

[yardwork]

It's time to replace the carpet on my stairs and bedroom floors. We're talking about 700 square feet, and I dread this because it means taking the beds apart and moving furniture, but it needs to be done. The underlying padding is falling apart and the carpet is worn, dirty, and has ripples in it now. I had it cleaned a few years ago and that's when the padding fell apart.

Should I work with a local carpet store, or is it safe to purchase from Home Depot or Lowe's, which seems to have cheaper pricing? What are the things I need to look out for in purchase and installation? I've been reading about the different types of carpet. I know that it's important to get good quality padding.

This needs to be reasonably priced, but I'm probably going to be living here for a while, so I want it to be good quality.

Thanks for any advice.