Library in school is often a quiet place, maybe a small area could be created there? School must show willing in resolving the issues with this for your DS....you shouldn't be having to fight for a quiet, suitable, pleasant area that DS can feel safe and calm within....it's their remit to ensure this is possible and provided and it's on his statement as a necessary need that must be available to him at all times.
Maybe school would be interested in getting a group together to give the space a make over, paint it, invest some funds in making it calm, cosy, and comfy, etc for all the kids who need it. Have a brain storming with the kids and decide on colours, furnishings, lighting, equipment, etc...might be worth a try to go about it this way, like a project which also incorporates their learning/education, etc??..maybe??
For my DS the support base room wasn't helpful to him either and actually made him more upset in many ways, esp sensory. It is often too busy with noise, people coming and going,etc. My ds sat in a corner with headphones on playing loud music and trying to block out everything else around him...not a good situation at all.