Well, you're missing some +lvls from staff, amulet, and vertex. Those extra levels give you quite a bit of damage. If you do get another chest piece, try to get one with 50% converted to life and then get a heart of well diamond with the remaining 2% to fill the gap, so you're off mana completely.
You could benefit from better rings as well. You should try to get one with cold damage, cast speed, life and whatever else you can afford. If you get one good one you can copy it with kalandras touch. Also good idea to put cast speed in your gloves socket. You want to stack cast speed where you can. More casts/sec increases your dps output.
Your jewels could use some love too. You can divine the good ones for better rolls, especially the one with cold dmg, dbl crit chance and max es. I woukd concentrate on spell dmg, double cc or bonus and max es on jewels. Not sure what your crit chance is, but i run my bm at 100%.
I know amulets are very expensive, so I would leave that for last? Try to get one with cast speed when you do upgrade. I would start with a +4 vertex and a good ring with cast speed. A new staff if you can afford an upgrade to +6. I'm not sure if you're running spark or deodres ew most of the time, but most people choose one or the other. If you want to stick with wand then you probably want to get rathpit and mana stack, if you're going with ew, then better staff for sure and stack life. Try to get your life over 2k asap too.
Iamjustanthony has some good bm builds where you can get good ideas.
