iam not sure can this design work or not but i want to share, it actually base from Dragon ball Chair design for the saiyan race but iam not sure is it made by.
finally found it
i dont know the original creator or notartist name though, but i cant found the image, so i use rough photoshop to this chair instead to help visualize it. on pinterest
so in the design it have a slit in the middle back and some havei suggest add a combination of a reverse toilet hole too (basically extend the slit to become toilet hole, to accomodate different tail angle to be able to just sit straightly or not sit awkwardly or without contort the tail or ass first while not hindering or hurt their tail when sitting.
original image from:https://www.diotti.com/en/hole-single-piece-polypropylene-chair.html
for visual image of the reverse toilet hole dont take it literal (some even reach to the middle part and big like toilet hole, i dont use toilet one asbetter image example because someone may get disgusted or considered it not approriate) but combine it with the slit design basically extend the slit to there, or you can just use this instead.
from: https://www.amazon.com/slp/chair-support-for-lower-back-pain/9uunpf37wnxx3r3https://www.indiamart.com/proddetail/hospital-toilet-chair-15480843597.html