Not everyone can use a mouthpiece. If your sleep apnea is severe, you'll only be able to use CPAP.
I have sleep apnea. I hated CPAP. It was recommended to me by a surgeon that I should have the surgery (uvulopyloplasty). I had redundant tissue in my throat, and my turbinates in my nose were too large. I had these cut as well (turbinectomy).
Bottom line: Do not get the surgery! For four weeks, my throat was on fire! Every time I swallowed, it hurt so bad, it felt like an electric shock going through me. What made it worse was that the surgeon (who was Black, as I wanted a Black surgeon) basically thought I was faking it. He was a real asshole. Because I didn't heal right, I had to get a second opinion, and that surgeon said that the surgery could have been done differently, and I would have had less pain! I didn't even want to eat, it hurt so bad. I lost 15 pounds. Although my sleep apnea was decreased enough for me to not have to use CPAP - I only had to use a mouthpiece - in retrospect, it wasn't worth it. I also had to have speech therapy, because my voice would fade in and out.
Don't do what I did. Just use a CPAP machine if you have to and keep it moving. If you're fortunate enough to have a diagnosis of mild sleep apnea, use the mouthpiece if your doctor says that's what you need. Keep your weight down.
Also bottom line - Use your CPAP or mouthpiece EVERY night.