Spoiler alert: Put a rubber grip on any cue you use as a break cue. Read to the bottom for an explanation.
You can use almost any shaft that is stiff and put a harder tip on it. I use a Samsara Break/Jump, which is leather that's nearly hard as phenolic, and it's a beast, but still has plenty of control. I can even run a rack with it if I have to. I've converted old 13mm playing shafts to break shafts with just a tip and they served me well.
Currently I use a Katana Break shaft (newly released product, around $160) I just popped it on one of my old playing cues and added a slightly heavier weight bolt.This has a very strong bamboo core and can deliver absolutely scorching CB speed because of how well it transmits energy, although this also makes the shaft a bit lighter and to see the effectiveness your technique has to deliver the full force cleanly, if you're off-axis with your hit the power escapes quickly.
A guy who usually does alright with a Predator BK2 grabbed my Katana breaker and put down 6 on the break his first try, I'm surprised he let me have my cue back..
But, especially as this is just for the house and you may have less experienced pool playing guests using it, whatever you go with, I'd definitely stay away from phenolic. Amateurs miscue the piss out of phenolic tips. Also when you want to have a good controlled softer break for 9 ball, that is very hard with phenolic whereas it's easy to still get a moderate-pace hit and draw the CB back up table for position with the Samsara.
I may even suggest you get a heavy sub-standard shaft (usually the wood is somewhat spongy on lesser shafts) that is NOT low-deflection at all, put a hard playing tip on it (not a break tip) and up the cue weight. Your maximum possible power will be lessened a bit, but that combination makes it very easy to drive the CB plenty hard into a rack every time even if you hit it a little (or very) sloppy.
Weight: similar to or same as your play cue,
I don't know that I agree with this. My playing cue is 17.4 oz, far too light to smash a full rack really well without the stroke going a little wild every so often.
Without getting into the whole light-vs-heavy break cue debate, I will say this: The flesh and bones in your arm weigh far more than even the heaviest beak cue allowed. Especially as gravity is helping you out when you swing the cue through, your ability to accelerate your arm isn't really affected by having a few extra ounces in the break cue. Really, your ability to accelerate the cue with control is not so much to do directly with the weight your arm can move as it is with the ability of your fingers to keep enough grip on the cue that it moves as quickly as your arm and doesn't lag behind, losing power and accuracy. You also certainly don't want to over-grip, tensing your hand beyond a certain point starts limiting the speed your arm muscle can contract. You run into trouble accelerating a heavier cue when it's so heavy you have to over-grip it, which reduces the efficiency of your arm muscles, so if feels like you can't move it as quickly.
So, you can use a heavier break cue and generate plenty of speed (and energy into the CB) if you can keep a moderate grip that won't slip. That's why I put my break shaft on an old playing cue with a rubber grip, I can keep my arm loose enough for maximum speed and control and there's still plenty of grip to get the cue through without it slipping at all in my hand.
There are even slip-on rubber grips you can buy for just a few dollars. They can really help your break, giving you more freedom to adjust your grip pressure, cue weight, and arm speed. That lets you get plenty of energy into the cue without throwing your body into it like you see a lot of people do, which requires tons of practice to do consistently. With a rubber grip I can bring a 20oz cue through just as quickly as a 16oz cue, without any more effort, and it translates to more energy delivered. So the correct weight is whatever your technique and grip will allow you to bring through as fast as your arm can do so accurately. Too little weight you may swing wild, too much and the cue may lag behind your arm or cause you to pull with your body off-center which will be inefficient at getting the power into the CB.
Unless you're a really, really heavy hitter, almost any 13mm shaft and ferrule will stand up to the punishment, but for maximum efficiency and peace of mind knowing that if you develop a savage break you won't obliterate the ferrule, you may want to look into a specially designed break shaft.