well, the touchtype does just that. it’s an ipad case that has a dedicated space for the apple bluetooth keyboard underneath. Of course it ads a little extra weight to your Ipad, but the touchtype has a few good ideas. here are a few photos of this case, but you can also go check by yourself the video on the kickstarter page, or on their website.
as you can see, it’s ain’t as bulky as one would have expected. only the thin part of the keyboard is under the ipad. But it ads an extra length and width, so then if you really need to type a lot, why not consider buying a macbook air ? prices are falling for previous generation, and apple refurbished product prices are great too, starting from 799$, it’s as much as the low-end macbook air.(I bought mine refurbished).