I have 2 1920x1200 and there is no reasonable upgrade except maybe something like 40" 4K (and not in retina/high dpi mode). 2560x1600 would be ok, but it's too expensive.
3440x1440. Less pixels overall than your current setup, but incredibly nice to use. Also affordable, you can get them for under $400 during sales / end of year clearance.
Seriously, for coding I absolutely love a 1920x1080 screen rotated 90°. Still wide enough to see an entire (sane) line, but more vertical space is just wonderful. Can't watch video, obviously, but for a work computer the vertical space is the absolute best. Improves web browsing as well for most sites.
I tried a 36", I can't stand it as a display. Fine for a TV, but it's a little much for a monitor. Although I can't stand more than 2 displays, so YMMV.
