Fought bedbugs for a couple months many years ago. Here's what worked for me:
Lost a couch and a bed boxspring since we didn't want to risk trying to salvage it. The only bedroom furniture we tried to save was the wooden bed frame that I took apart every time there was a sighting of remnant bedbug during the weekly check. Put the mattress and boxspring in a nice bedbug proof cover (don't get the cheap plastic stuffs, it will just tear and make too much noise during sleep and you'll end up buying it twice). Kept furniture and bedding in the infested room to minimum and 2 ft away from walls and put DE around the walls perimeter. You don't want them getting into the walls and infect other rooms but it would have to be a major infestation to start getting into walls. I only had the bed and simple night stand left for easy clean up and cleared out all tables/books/dressers/closet. Our sons spent 2 months changing clothes in another clean room and only slept in that room. Moved all the rest of the furniture into garage storage during the treatment. Did the mattress check daily/weekly for any signs and if I see them, time to take the bed apart and clean every nook and cranny of the furniture and vacuum the entire room. I ended up taking the bed apart to clean 3 times and the third time, decided to paint over corners and crossbars with a layer of acrylic paint to seal in any possible hidden place in the cracks for them to hide and lay eggs which seems to have done the job. The check and clean rinse and repeat took 3 months before I stopped finding trace of bedbugs. It's been said that you don't really get rid of bed bugs until you stop seeing them for 6 months. Every time you see one, the clock resets. The chemicals are useless since they don't really seep into cracks where they hide and lay eggs. My only chemical used was 99% alcohol in a spray bottle for instant visual kill.
I did look into getting exterminator pros but they start at $500 and can run up to $2k and they also can't guarantee you won't get reinfected. You end up doing most of the work anyway with isolating beddings and laundry. I did that making sure everything gets into extended drying cycle and stuffs in separate bags and stored in plastic containers. That one encounter with bed bugs scarred us all pretty good and now whenever we go to hotels, that's the first thing we do is check the hotel mattress for signs.