Hi there,
Welcome to YorkieTalk.
Milo is quite young. I bet he's a total sweetie. Have you considered using a good sized X-pen for him? At 5 months, my little one spends most of her time either in the X-pen or on the bed. She has a pee-pad in both places. She just doesn't have much opportunity to make a mistake. If we haven't spotted her good deeds right away, she'll let us know and gets a verbal reward and a treat.
My yorkie experience has been with two pups 12 weeks +, both of whom grew to or will grow to weigh say 5-1/2 pounds +/-. They were/are both old enough so that, within short order, I was able to schedule their feedings--which becomes a pretty good indicator of when they need to use the bathroom.
Both of my yorkies were/are being trained to use a pee pad for potty. My late sweetie usually needed to poop once a day, and she did that while she was walking in the morning. My current baby poops twice a day--once about 5 am--an hour or so after she wakes up and again between 5 and 6 in the evening. She's still doing her big business on the pee pad, but as our weather evens out a bit here, I hope she takes to doing that business outside.
A few links
WebMD, "
House training your puppy."
PetMD, "
How to potty train your dog."
AKC, "
How to potty train a puppy: A comprehensive guide for success."