Its a relief to read this response as I feel like his behaviour is constantly blamed on myparenting and (particularly from grandparents) and it’s a lot of pressure to be trying so hard but getting nowhere
I doubt very much it's your parenting, especially as you're so motivated to help him. I'd start trying to turn a deaf ear to any criticism. I'm not saying your DS is ND but if he is then people who've had NT DC often just don't understand how different it is.
tbh I am really hoping the school do suggest an assessment as I think that’s the only thing that will change how my partner and the rest of the family perceive him and treat him. If he is ND we are going straight to parenting classes to help learn the best approach to parent him.
I think the biggest thing my DC have from their diagnosis is understanding of why they are like they are.
his diet isn’t very high in protein as he won’t eat a lot of meat or pulses. He does have cheese and either yoghurt or milk each day. He mostly likes to eat fruits, raw vegetables (although fairly limited range, maybe 5 or 6 types he will eat), and carbs like pasta, rice, toast, cereal. I’m sure a better diet would help things but not sure how to get it in him! He is likely eating too much sugar through all the fruit and carbs.
DC has Food Avoidant Disorder previously known as ARFID so I can totally get limited diets 
lots of time to regulate as he goes to a tiny free school with a lot of emphasis on outdoor learning. He loves dog walks and being out on his bike. We go skiing once a year and that’s the happiest he is all year. Now you’ve made me think about it, when he is doing non competitive physical things is when he is most regulated
If he's best when he's skiing is there a Ski slope nearby that does classes at the weekend? Mine both liked Cricket. Although it's competitive it's more geared to being part of a team and there a lot less physical contact than football or Rugby. Perhaps have a look at your local club around April time to see what they have on for their younger players
Hockey is usually on this time of year. Our club does a Saturday morning session for the smaller ones which is enjoyable and they lend you the sticks.
It's hard to get the balance right though between doing activities that regulate and downtime so that they can recover mentally 