My doctor at the sleep study suggested something similar, she specifically mentioned asking my dentist to get 1 custom fit. I'll probably go that route whenever I have my next appointment.
I’d try this first. You mold it to your mouth when you buy in so it is “custom” technically. Plus, it’s $40 and if doesn’t work for you, you can send it back. A lot cheaper than going to your dentist. It works great for me (I’m on my second one).