Voltage regulator and Amperage question...

[cr.chango]

Hi to all, this is my first post here and I'm very happy trying to get my question addressed by you guys.

I have a Yaris hatchback '03 1.3L, 103000 km... recently I have had ignition issues, the engine didn't start a couple of times
I called assistance and got a (+)(+) (-)(-) to charge my battery, but I knew I had another problem.

My first thought was the battery, so I checked it and it was OK...
with the engine started, the voltage was very low 12 V (I don´t have the exact value at hand), so the problem was redirected to the alternator...

So, I had my car checked by a specialist and he told me that the problem turned out to be the voltage regulator...

Here comes my first question: is it better to buy only the voltage generator, or would it be better to buy the whole alternator???

It has been very hard to find the part and the only ones I've found are Nippondenso, and I really don´t know what to do...

The second question is related to the research I made trying to find that volt regulator and it´s about the amperage of it...

How do I know what the amperage of my Yaris is? I asked to an expert and he said that it was 70 amp... What if I get a 80 amp volt regulator for my Yaris, would it cause any problem???

Thanks for your attention, and sorry if I was not quite an expert... 'cause I am not!