First of all, don't pay for any replacement parts for the Mini. Empire will replace anything for free and have it to you in 5-7 days, even if you bought the gun second-hand.
Are you having breaks in just the barrel or also in the breech? Early gen Minis had different detents than the newest V3. Make sure you have the new style detents because your loader could be double feeding and causing breaks. You might want to check what version poppet you have while you're at it.
As for a barrel, depending on the average size of your local paint, I'd suggest the Lurkers Eigenbarrel. I use the .678 bore almost exclusively on my Mini with great success and no barrel breaks. Empire : Paintball Solutions
You will find the manuals at the link above. Use the Mini manual if you have the Optimus board. If your Mini is newer, it might have the Empire Shockwave board. You will have to use the proper manual depending on what board you have. Check inside the front grip to see which you have.
Make sure your dwell is at 8ms, pressure between 180-200psi, and backcap ~.75 turns out.
I also agree that the stock trigger is the Mini's weakest point, but have to disagree on the the magnet return being inferior to spring returns when dealing with aftermarket triggers. Empire offers a trigger that's very similar to the one on the Axe. They have adjustable magnet return and are only $16. The Violent trigger comes with 3 different sized magnets that fit into the trigger so the tension can be adjusted and a lot more features that the CP trigger lacks.