The phrase
Animals must be large enough to be safely mated with is mentioned among
the rules for a reason. There is a grey area depending on your size and the dog's size, but if you already describe him as "small", then it is unlikely it is safe to do this. Apart from the trauma for the dog, how would you explain injuries to a vet? Also, "getting him to like it" and "getting used to it" very much comes close to training where you easily end up with learned helplessness than with mutual consent.
In conclusion, if you both like what you're doing now,, just stick to that. It's better for your dog's well-being and for the relation you have.