Is there any particular reason why you are thinking of a dog as the best option for you?
While useful, and frankly amazing, I think a hypodog would be probably harder to get and less reliable/effective than a rtCGM with alarms.
At least with those you can check your glucose levels at any time, and if you see a downward trend you can act early to avoid a hypo before it has happened.
They do have a cost, but then with food bills, insurance, and vet care so does a dog!
Another thing to beer in mind is that having a service dog is not the same as having a pet.
They have to know when they are on duty, and you can’t just allow them to ‘play’ or do normal pet dog things whenever they want to.
My feeling would be that if you want a dog, get a dog, and if you want a glucose sensor to alert you to hypoglycaemia get one of those.