You gotta get your stam pool up a bit. In Cryo I run at close to 16k, and in BGs its like 13.5k. There are lots of ways to do this. In BGs especially, you have to build for sustain first. This is all with witchmothers drink.

The most obvious is Shackle, 1 Piece Domihaus, and Tri stat glyphs on your infused big armor pieces. You can even go with 1-2 tri stats on jewerly (i found 3 to be over kill).

There are really Three basic ways to build with shacklebreaker. I highly recommend shackle as your main set until you are more comfortable. It's hard to call things meta in PVP, but shacklebreaker and sorc is about as meta as you get.

First: If you want a ton of sustain, pair it with Amberplasm (seducer or lich could also work here), and set it up so you have 5/5/2 at all times. Your monster set can be engine guardian (max sustain), one Domi + one Grothdar (max stats), Slimecraw (max damage), Balorgh (max burst). Certainly others are viable. I most often go for the stats. This will give a ton of stamina and a ton of sustain. This is pretty easy to do because you can make shackle weapons. Just need a bit of normal ROM farming for Amber, or the ability to make some jewelry.

Second: Use an offensive set on your front bar, and either a willpower or VMA resto on your back bar. Sets like spinner, Sloads (gives extra stam), Moon Hunter, Caluurions, etc. Lots of good options here. Only trick is that it takes getting the staff in the set you want. This is a good option if you have good group support and want a little more damage.

Third: Run a defensive/sustain set on your back bar and front bar either a willpower or Asylum Destro. Same issue, but this time you do need a resto in your set of choice. Obvious sets are Lich and Riposte (just nerfed). This is perhaps better against better groups where you either need a little extra sustain for longer fights, or you need a little extra defense for those hard hitting stamboys running around.

You will find that different situations call for different things. If I am alone in BGS, I go max sustain. If I am with a good group that is being aggressive, i go the second option. If I am really in an even match against another good pre-made, I find myself going with option 3 sometimes as well.

Edit: One thing I forget to mention was potions. Seems obvious, but they go a long way with stam. I carry all the good ones, but honestly, the one I drink the most on my sorc is the stam+ major expedition+ imov pot. I have good control over my magic already, so the stam recovery and mobility are great. In BGs, I also use a lot of tri-pots. In cyro, detect pots and magic+crit+imov are also nice for when I want to track down a NB (former) or go all out damage (later). If you arent drinking potions on cooldown in combat, you are at a disadvantage, because I assure you, the other guy is.