Here we have the three main altars. The Image of the Day is of the altar of the center nave, and if memory serves me well, the image to the right is of the altar of the former right church, and the image on the left is of the left church.
Like seen so often in Italian churches, you can switch on the lights by inserting a coin. That’s what I did and what I’d recommend. Otherwise you’d miss out on the rich colors.
Even so it’s pretty dark. Thanks to the in-body stabilization of my camera I could use base ISO 200, but for the image of the right altar I was already at half a second. I suppose you could use a tripod, at least I have not seen a sign banning them, but I always prefer to cope without. It’s much less intrusive in a house of prayer. In any case forget about flash. It’s forbidden in most churches and museums.