Conditioning before returning from injury

Hi,

I'm on the verge of returning to the mats after being out for 3 months. My cardio has always been a problem and i'm looking to get a bigger gas tank. That said, i've never been able to get into jogging so im looking at other forms of steady state cardio.

what is your goto for steady-state cardio?

i've been eying down jump rope for the most part