If you sat on your glasses, you probably would need new lenses anyway

I have sat on my glasses many times and I don't need new lenses each time. Lenses are way stronger than any frames. If you don't scratch them - like if you sit on them with pants wearing keys in your back pocket - they're good to go on replacement frames

do you have a second pair at home?

No. Just the ones.

Well, I have a pair of progressives with really expensive lenses (only one) and 2 pairs of cheap single-vision near glasses. But the one pair I need most - and care about the most - is the progressives.

Or does the round shape mean that you could just order it online because the shape is so simple?

Actually the shape isn't that simple. It's not a circle, it's an ellipse.

But regardless, you can't order lenses on plans, sadly. All lens cutters use edging machines that trace the contour of your frames and edge the lenses accordingly, because almost nobody orders lenses without frames. That's why I supply a model for a 3D-printed template to supply to the lens manufacturer in my Github. If they took STL files, it wouldn't be needed, but they don't.

I have had glasses for a very long time and never broken a lens, but I have broken more than my fair share of frames. It takes a lot to break a lens, and plastic frames break pretty easily. The worst with lenses is scratches or chips (though chips are also rare for me), and some of that can be mitigated by cleaning with the right cloth. Not much can be done about drops or other accidents though