The most preferred scope is to connect normally. Floating the scope is the last thing you would want as an alternative.
You are potentially putting line voltage on the case of the scope and bad things can start happening very quickly, this could impose a risk of life too.

We suggest you look at the wiring diagram and decide where the grounded conductor is and ground the scope at that point. The small amount of ripple you see will not affect your measurement. It is tied to the ground via an external plug.

If you are looking at something on the load side of a transformer you should be able to ground the scope normally. You can ground the scope to the circuit through a light bulb, voltage wise. If it sparks, you are going to have to reconsider your plan of action.

Be sure you have the right ground clips if you are looking at line voltage.
It is best to learn your scope technique with a transformer isolated circuit, preferably at low voltages, like a doorbell transformer or a wall wart.

Electrical companies can provide the necessary advise based on the requirement and concern with the floating ground.