What's the resolution of the ultrawide?
I'd personally move up one step at a time. Operating on 1080p for however long you have been, and then suddenly make a huge jump and slap a 4k next to it... I would think the image quality between the two would make things a little disorienting.
Ultrawide pretty much reduces the need for multi-monitor setups, or that's how I see it, at least. So if you were to get that, then sell off the old monitor or something.