I was really ill a few years ago and couldn't look after my dog. He was a rescue dog who could be aggressive with strangers. I hesitated but really had no option but to put him in kennels for a few weeks. He was a Lab/GSD mix so not a small lad.
He loved it, he was a good boy and played football with the young lad at the kennels. He went there a few times after that.
Dogs Trust do have a scheme where you can sign up for them to take care of your dogs should anything happen to you, but they don't do temporary 'boarding' as their kennels are full to capacity with people dumping all the dogs they bought during lockdown and now can't cope with once they went back to work or didn't realise what a commitment having a dog is. I would make contact with a local boarding kennels or more likely a dog sitter so you have an arrangement in place should you need to leave him for a short time.
Just thinking, didn't you get him from a rescue centre? Could they be contacted for back up (which is what my breed rescue does for any dog we rehome).