I use the Impact brand, mouth guards.
https://www.impactmouthguards.com/collections/stripes-flags/products/white-red
The link above is for their 2-color style, but they have a lot of options.
That particular one costs $59.
Under the pulldown menu where you choose your sport, I have a couple for boxing and one for BJJ.
The only difference in those two versions is the thickness in front of your teeth.
The Boxing one is thicker than the one for BJJ.
I am able to talk easily with either one. I keep them in the whole time. Not having to remove the mouthguard is a plus from a cleanliness perspective. Touching the guard to take it in and out is not a good idea. These you can keep in all the time. They don't impair breathing or talking.
The link above is for the style that you have to make a mold/impression of your teeth and mail it in.
so it might take a few weeks to get your mouthguard.
They do offer a boil and bite model. It costs $29.
I couldn't tell you anything about that model. You'd have to contact them to ask about how well you can talk when using their boil and bite model.
My son has one that I ordered when he started BJJ. He later used it for a season of wrestling. He kept it in all the time also. He never felt it interfered with speaking.
I hope that helps.