IMHO a smart regulator for the alternator won't do you much good with only 35 amps capacity anyway. Not sure what engine
you have, but most could power a 90-100 amp alternator. I've had good service
from standard automotive Delco 12SI alternators you can get at any auto parts
store. They're rated for 94 amps. Even with the standard built-in regulator they put out a lot more juice than your 35 amp alternator. I get mine at Advance Auto and they have a lifetime warranty. You've got to figure out what car they go with, as they only source parts
by the car. Make sure you don't get one of the so-called "one-wire" alternators--you want one that can sense the voltage at your batteries, so it has a separate wire for that. If you have a gasoline engine
you need the kind with a spark protector on the back, but for diesels you don't need that. There are also some reasonable Leece Neville alternators which are even better, but cost a bit more too.
I will add that I would highly recommend putting both of your batteries in one bigger bank for the house supply and routing all charging
sources to that bank directly, or just keep that switch on both. The less percentage you take from your battery
bank the longer it will last--less deep cycling. It would be ideal to add a third battery
dedicated to engine starting that is charged by a combiner or a Trik L Start or an Echo Charge. The Trik L Start is the cheapy way to go--mine has been working for a couple of years perfectly. That starter battery is just used for starting the engine. If you don't want to add the batter, be sure to keep an eye on the voltage in your main bank so it doesn't go too low to start the engine. Lots of threads on this if you want to do a search.