Have a look on classifieds for Minki Yoyo nappies (and maybe google them to see if any sights have a few left). They have recently stopped making them but I've heard they are fab and can be stuffed with extra such as hemp which it sounds like your LO needs as super absorbent.
They stopped making the yoyo?! I had one which worked really well - Jaden was 5 at the time - but I'm pretty sure I gave it to my friend for her autistic son. But I am moving in a couple of weeks so I'll pm you if I find it @bugglyboo