What type of subwoofer?

I want to build a passive sub but the dimensions will be a bit limited due to the location in which it will be used, basically tucked between two large bookcases. The maximum width has to be 220mm and the depth 300mm. However I could probably go to 1000mm in height. There is plenty of design software out there but I would like a push in the right direction with regards to what type of design I should be looking at, ie, ported, transmission line, sealed etc. Because of the position it will be used in, all ports, drive units, horn apertures etc need to be on the front or bottom of the unit. Any help appreciated.
Back of the Voxativ Ripol and video (@0:15) factory tour.


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If the bookshelves are on, or near, to a wall, the ripole design is likely one of the worst choices. That's a dipole bass design and needs to be away from any boundaries to work best.

The 220mm limitation on the width suggests that the drivers will need to be fairly small, like the Tang Band 6.5" subwoofer drivers, for example. Using one or more of these in a slot-loaded subwoofer should work, depending on how much output you're looking for.
Maybe I am asking for something that is difficult to achieve. It seems that what I am going to end up with is effectively a floor standing speaker but with only bass units. This is no too much of a problem as I am only looking for some bass reinforcement and not ground shaking home cinema bass. I have recently had to (temporarily?) retire a pair of floorstanders and have bought an oldish pair of mission bookshelf speakers out of retirement. I am really just trying to regain some of the low end I have lost.