You want to be very careful with any muzzle that restricts the opening of the mouth. The danger of heatstroke is very real.

And yes, you are paying now for not going to puppy class early. Better late than never.

Personally, if I had a dog with whom barking was such an issue, I would have the dog surgically debarked and forget about it. Then the dog can bark all it wants without really bothering anyone. It certainly does not bother the DOG. They whisper bark away without a care in the world. They just dn't annoy people any more.

this is one of my all time favorite links about how to be the pack leader for your dog.

http://www.sonic.net/~cdlcruz/GPCC/library/alpha.htm

Dogs do not think like people, and you cannot raise a dog as you would a child. You are likely sending this dog a lot of mixed messages he can't figure out.