Speaking about ryokan - a friend visited one with an onsen attached and he was not really pleased
Believe me, traditional Japanese environment is definitely NOT the best setting for a holiday and is totally not romantic, private or luxurious...
My friend was in a first class ryokan and he said that actually only things he had in the room were a table (50 cm high) and something like "a bed from dried rice paddies" or something like that, and the room was not single, not double... there were 4 people in one room
The onsen was divided into men and women, so I dont think you wud be able to enjoy with your husband, and furthermore, meals were extremely small (as they are everywhere in Japan) and there were gokiburi (Japanese cockroaches).
I hope that will make up your mind for a traditional Japanese adventure...