I'm thinking of trying TSS in a Remington youth 20ga for turkey this season. A nice light run and gun type gun. Any advice on shells or chokes would be appreciated. I'm thinking of #9 shot and I don't want a super tight pattern for when a close shot presents itself. I have read a factory full is a good place to start, but my chokes do say lead shot only.
Carlson’s and Müller make chokes suitable for TSS. I’ve been using a super full turkey choke (.650 diameter) in Benelli SBE3 12 bore with incredible results. As you have stated, it's much like a rifle shot at close range, so it's best to do pattern testing at different distances. Contact either (or both) of these companies for the details. Both have very good customer service and I've been very happy with them and their products.
The other alternative is to use an over/under with two different chokes and two different loads. This is what a friend of mine is doing in a Browning Cynergy 12 bore & 3.5" chamber. He loads the bottom barrel with Federal Premium Heavyweight TSS 3.5", #7 shot, 2 1/4 oz, 1200 fps using a TKY choke that's good out to 70 yards. Top barrel is Winchester Last Call TSS 3", #7 shot, 1 1/4 oz, 1500 fps with a SKT choke for shots up to 30-40 yards. He also happens to be using a RDO on this rig because aging eyes suck.
This option would give you solid patterns from 10 yards out to at least 60. I've found the Browning Cynergy to not shoot quite as tight as my SBE3 which has killing capability with this load out to at least 70.
As for the particular shot size, that's your choice. From personal experience, I've found that #7's work wonders on goose. The anatomy of a turkey is quite similar when it comes to them floating in the water or walking on land. I've seen TSS #9's in YT videos taking all manner of game, but I'm not sure of the distances, loads, chokes or shotguns they were using. #7 works for me, so I'm sticking with it.