yes, you can get wedge cushions through the senco as well as arms for the chairs to stop him falling off. My six year old has dcd, as well as having other sen issues, and these things are being ordered as well as pencil grips and writing slopes and for my son the list goes on and on.
there's also straps that can go on chair legs for the children to play with with their feet. Also your child may need movement breaks. Lol, unlike MrsLettuce, my son falls off everything, including his chairs.