Just make sure you don't buy a cheap
eBay alternator. They advertise a higher max output but almost always put out less amperage at idle than your factory alternator will. Many also have questionable quality rectifiers and diodes.
A few popular and equally high quality brands have been listed. Autotech, JS, Mechman, Singer, & others all make good alts.
I have personally seen an alt fail from every single of the top companies at one time or another... it's just the nature of alternators unfortunately. Basically, I like all of the good ones equally.
I'm not familiar with your vehicle, but depending upon the physical space available, a large-case universal alternator may be an option, but like others have said, you will have to get custom brackets and likely a 1/2" shorter belt.
If all of the reputable companies that make a high output alternator for your vehicle all have a max output of ~200 amps then there is a reason for this. There is no magic alternator - the factory size casing for your car is physically a certain size and you can only fill it with so much flat-wound copper and you can only make a pulley so small before the belt will start to slip. Reputable companies respect the laws of electricity and physics to find a balance between these factors that give you the most usable output.
The best alternators will have a high idle output and reach maximum output at a reasonable engine RPM. Alternator power is useless if you have to be revved up to high RPM to actually achieve it.
Electrical upgrades get expensive rather quick, and don't forget you're going to need to run bigger wire also, as others have mentioned. Many smaller cars come from the factory with 8 gauge wiring. If you're going thru the trouble of doing this, I highly suggest using 0 gauge wire for everything.
Depending on what your costs end up being, it may end up being best to use the ~200 amp alternator combined with some lithium iron phosphate cells. This is a whole different topic, however, and I'm not going to go into it. Maxwell Supercaps are another additional topic in addition to this one.
Personally, I would just buy the best available alternator I can that preferably uses the factory mounting. Buying a new belt is usually cheap if it has a smaller pulley. Then I would try it playing the system however you normally use it while monitoring your voltage, and then you can proceed from there based upon your results.
Either way, an alternator is the best single electrical upgrade you can make.
One last thing, when you upgrade your factory wire you do not need to remove the factory wire. More wire = better. Run the new wire right alongside the old wire. This is also usually easier. Just make sure you get OFC (oxygen free copper) and not CCA (copper clad aluminum).
There are several good brands for wire. Personally, I like using Knu Konceptz. Recoil Audio wire is also true to spec, but they don't have the fancy colors that Knu Konceptz or Sky High and others do, if that matters to you at all.