I read about DLD's
SRT routine and stretching would be great to do after ejaculation, as the penis is fatigued and very easy to stretch.
From other stuff I've read, I've noticed that lenght / stretch excercises would be done before girth workouts.
And cock rings, so much to choose from! Some are meant for your whole unit and others just for your penis. I'd try to find a ring that has some width. Silicone is a good material, don't have some much experience in latex rings.
Say no to these jelly rings etc., they'll break after couple of times or the first time. Really incompatible with many good lubes as well. They're maybe alright for one-night stands, but for serious workouts and long time use, no way.
Adjustable cock ring would be your best bet right now. That or you could buy a set of different sized silicone rings. You'll usually find an adjustable cock ring for under 10 USD.
Don't be afraid of those weird fetish sex shops, they usually have great selection for the not-so-weird-and-fetish oriented. Definately don't be afraid to go into these shops. Might be embarrasing at first, but you'll get over it.