Advancing In Our Chastity Lifestyle

Sooo.. I popped the question to my Goddess. Nooo, not that! I asked her her opinion and thoughts on moving toward a stainless steel chastity. I know! Most of you are wayyy ahead of me but.. I currently have a sissy pink Bird Locked (BL) classic with the 40mm ring that we have used since September 2012.
I brought this up for many reasons. I suppose if you are going to be serious about this lifestyle you need to have the real deal. The BL is easily defeated and I have slipped out while sleeping and sometimes when I crouch down. One time it even slipped off while I was on the ecliptical at the gym. I felt it slip and caught it before it fell out of my shorts. We learned that it cannot be used at the gym due to the nature of my workouts. Aside from chaffing after prolonged wear, I highly recommend it as a great starter piece. It's difficult to stay clean and dry inside after using the bathroom due to the ball strap. Otherwise it serves the purpose I suppose.
Another reason is because since entering chastity I admittedly have cheated because of my selfish sissy urges. I feel absolutely horrible when I have done so. Lady Jessi tells me to talk to her when I'm having these thoughts and she will help me through it but it often times occurs at night while she's sleeping. I NEED something I cannot defeat. When I brought it up she mentioned having no room for growth. That is something I have wished this one accommodated. Even with the little room this allows when I start to grow, it continues because of the extra room and causes quite a strain on my sissy bells and begins to cuts of circulation. When I grow, I grow large. When I'm small, sometimes it's... laughable. Even I've been amazed! With all this said, I need some help with sizing.
I measured myself according to the instructions on Lori's website and came up with the following +/- 1/4":
Flaccid Length: 2 3/8"
Shaft Diameter behind head: 3 1/4" (divide by 3.14)= 1"
Shaft/balls Diameter: 7" (divide by 3.14)= 2 1/4"
My MAIN concern is the spacing between cage/ring gap. IF I would start to grow, if there isn't enough room it'll almost instantly cut off circulation. Ring style? Round or Oval? I've only had experiences with round thus far. Cage length.. I think the BL Classic has a total sheath length of 3.7 inches (95mm) and actual sheath length for my clittie of 2.53 inches (65 mm). This is about a 1/2 inch too long IMO. I'm thinking two inches is just about perfect for its flaccid state with zero room for growth. I think Lady Jessi and I both agree this is very important. I also feel that any urges will quickly subside because it cannot become excited to begins with. But again, I'm mainly concerned about that darn length between the cage/ring gap. As it stands now when I grow that gap allows for some additional distance/growth as it begins pushing back into my body if that makes sense. BTW- I'm uncut so I guess that plays a small role. Any sizing comments are greatly appreciated! Also, manufacturer and model suggestions are nice as well. We are not really looking to move toward belts or anything pierced at this time. Although there is a piercing that I've seen recently on the underside of the balls that had a dangling chain that would be just adorable hooked to the end of my clit. *melts*