"Large expanses of flaky wall" needs a simple roll of backing paper. If no budget for that you can use wallpaper but backing paper is better.
Ask if you can go into your local Primary School and look at their displays - there are experts in every Primary school I've ever been in.
Get in touch with your local CAMHS for some posters
Try other charities such as MIND, Samaritans, Women's Aid, Young Minds, Forced Marriage Support Groups, Prevent Training, NSPCC, etc
Then charities such as Dyslexia Association, and find positive images from all sorts of charities - Cerebra, Scope, Barnardos, MENCAP, National Autistic Society, Down Syndrome Association, NDCS, etc etc
Then those that increase accessibility and also acceptance, like Makaton, or SIgn along with us, or Wouldn't Change a Thing, Connect the Dots to ACES, etc.
Go to the Mighty Girl Website (or look for them on Facebook). They are a BRILLIANT resource. Have all sorts of downloadable posters and resources all about pioneering women - in science, civil rights, maths, education, war heroes, politics, and so much more. If you like their page on Facebook, you get regular information into your feed that will make you ask why the whole world doesn't know the stores of hundreds of women who have achieved so much over the last 150 odd years.