Denise,
defore you start looking anywhere else you should take Ady's advice. Service Record and medals allocated are an essential starting point.
No point going to Kew if he was never registered as a POW; which he doesn't seem to have been.The WO 344 Series is very incomplete, especially with reports from Military POW.
He is not listed as ever being a prisoner of the Italians nor is he on my POW lists compiled in 1944. Ancestry lists are those compiled in 1945.
There are many possibilities from the information you are giving. He could have been repatriated due to the severity of his injuries or he could have been left in Hospital when the Germans retreated.
All pure speculation, but I really would follw Ady's advice.