Hi and WELCOME to YT
. Glad you found us.
First, I am so incredibly sorry for the loss of your dear Louis. He sounds just precious, unique, and like he was one of the loves of your life. What a special little fella!
As for male vs females, I have 2 males and 1 female and love them all. I do think the males are more affectionate to a certain degree and many others say that as well here. But you can't go wrong with either, ya know?
I don't have any experience w/ training a service dog, so I can't really comment on that aspect. But a rescue may have the perfect little trainable adult for you, who knows....there are so many good rescue dogs out there. There is a member here named LadyJane who is with Yorkie Haven Rescue and maybe she'd have some ideas for you.