I bought my rig last year and needed to deal with extra power for pretty much the opposite reason. I don't use it everyday, and it sometimes sits in a cold, northern Utah garage for three-four weeks without starting. If I know it will be a while, I use a trickle charger on the primary battery. But I sometimes forget and then I show up and start plowing, which hits the battery.
In making my decision I read a bunch of the helpful comments on this site and chose the True Isolator ($129 with dual voltmeter kit) and a Might Max second battery. I'm a desk jockey with passing wiring skills. It was simple, even without resorting to YouTube. I've never had a problem and the isolator has a circuit to bypass if you need to. It was my preference to keep the accessories on the second battery, not the main.
Switching between two different batteries will work. I know what Bumpern is getting at is that two batteries in parallel will detract from each other unless they are essentially identical in age and make. Basically, the weaker battery in parallel will drain the stronger one. An A or B battery switch will avoid the parasite drain, but you'll need to make sure your trickle charger works for both batteries. Good luck. 👍