Is there a good tip to ensure your Lasagna does not fall apart when cutting into squares?
Have you tried letting it rest for about 10 mins or so before cutting?
Lasagna usually falls apart because there is too much moisture where the filling is too liquid and loose. I would suggest making the sauce thicker and using less cheese, in addition to letting the lasagna cool down almost completely. Lasagna is not one of those dishes that do well straight from the oven. Restaurants often have it already cooked and cooled, then heat to order.
I think the moisture issue is a problem. Try draining the ricotta (using a coffee filter is an option) before using.