Bicycle Mechanics - How do I know what size cross levers to buy?

Forgive me if this question has been asked, I'm new here and couldn't find anything with the search bar.
I've just gotten into cycling as someone who basically couldn't ride a bike a few months ago and have been customizing/fitting my bike. I bought a Tunturi 500r road bike (there a couple other threads here about the bizarro Finnish bike) and want to get cross levers. There are different sizes of clamps, how do I find the size I need? Also are they difficult to install?

They clamp onto the center sleeve or bulge of the handlebars, that is what you measure, on your bike.

as to how to fit them, they work by spreading the brake housing relative to the cable that passes thru the levers uninterrupted.

Un-tape the handlebars, disconnect the brakes, at the wheel .

pull the cable out , you will be cutting your brake housing.

then filing the ends smooth,adding ferrules on the ends

then feeding the cable back thru the new brake levers and the short piece of housing , and re adjusting the brakes.

Thanks so much. Do you have any experience with them? I know suicide levers are considered pretty unsafe and most people remove them (so I don't want those), but I don't like riding in my drops in traffic. That's basically what these are for right?