There's been some mention of "yoga chairs" in the past. I don't think there's a running thread for this sort of furniture and I came across some interesting options linked below. I intentionally ignored inflatable options as well as foam bits for use on a bed or the floor. Feel free to include them if you'd like or any others worth a mention. I flagged the links with a trigger warning as needed. These seem expensive for what they are, especially compared to the imported yoga chairs. A problem with all of these is usability is somewhat dependent on body size like all furniture. Buying online is less than ideal, but I doubt there are too many sex furniture showrooms.
- Butterfly Settee: http://www.butterflysettee.com
- Essence Chair: http://www.revelfurniture.com/the-essence (*trigger warning)
- Archer Bowchair: https://www.bowchair.com (*trigger warning)
If you're interested in art more than the practical, http://www.balastudio.com designs limited edition pieces. Look under Projects>Erotics as I can't link due the use of Flash.