We’ve always had bullhorn bars for the stoker, and they stick up well above my saddle. I don’t try to swing my leg over them as I would if I was trying to mount or dismount like I would my single bikes. Instead I either step over the captain’s top tube, or alternatively, swing my leg over the captain’s handlebar.
I bought this bar a few years back:
https://www.aliexpress.com/i/2251832...apt=4itemAdapt
It can be ordered in 46 cm width.