I think a tennis ball is a great 'catch' toy...light enough to catch with ease. Just don't ever let your dog chew on it. They do come apart easy. But we use tennis balls....I've mention this before, Addie is to be envied from pro baseball for her ability to catch a fly ball.
If you're always there while playing catch..I wouldn't worry about the dog swallowing the ball........more likely they'll spit it out when tiring of the game.
Hey, Big...I gotta agree that 6 wks. is so young...any way you can let the pup stay with it's mom til 8 or 9 wks??? (and, yes..I know this would be difficult for you!..totally understand that.
) IF the person you're getting the pup from won't have it..........then I'm glad that little baby is going to you. Do read up on how to handle that situation...you're gonna have to fill in for 'mom' in those critical weeks.