you need a monitor that is 3360x1050 that has the same vertical screen height, about 13" tall.... but this resolution doesn't exist. the 1050 pixel height is pretty darn close to 1080, about 3%, so if you buy a monitor that has a roughly 13" screen height your image will roughly appear about 3% smaller on the 1080 pixel height screen. most 29" 2560x1080 monitors list a screen height of about 13", most 23" 1680x1050(and 1920x1080) monitors list a screen height of about 13". there is a small scalling factor from a 1680 pixel wide to a 1920 pixel wide, but its very small, but the pixels per inch is quite a bit more, about 17% more pixels per inch.
a bunch of math. if you still want the wide feeling effect of two screens your best bet is a single ultra wide monitor period. im guessing you dont want the text to appear smaller than it already is and if not your best bet is to go with a 34" ultra wide. if you can tollerate things slighly smaller then a 29" ultrawide will do fine. if you dont want a 21:9 ratio ultra wide monitor and just want a standard 16:9 monitor then a single 24" 1080p monitor probably would be best bet if you want it near exact the same size, but a 27" 1080p would make the objects/text bigger by about 10%. this is all assuming you are always sitting the same distance away from the monitor.
is there a specific monitor you are looking for? go to a local best buy and purchase a 29" ultra wide, probably $200-350, though the $200 price is closer to a slick deal. you can return it very easily, but at least you can plug it in and see how your eyes feel with it. then later find one on a good deal.
here is a link to an expired recent excellent deal on a 29" 1080p ultrawide that was at bestbuy around christmas time...
https://slickdeals.net/f/10898559-bestbuy-lg-29um60-p-29-ips-led-ultrawide-monitor-179-99
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