While I can understand not wanting to spend the money for a sleeping car, I would really recommend it. Figure in, your meals are included. They are usually out of my price range but I have splurged a couple of times and they are worth it.
I don't find the coach seats comfortable during the night. I must have long legs, I cannot use the leg rest. I have to just use the foot rest because there isn't any room for my feet or legs with the leg rest extended. I also find the seats not good on my back.
With two of you, at least you can lounge on each other.
For my trip coming up, I will be in coach, wishing I had a sleeper to stretch out in.
But, I take a travel pillow and use the pillow they will give me also. Also an eye mask to block the light and earplugs. The coach cars are not very dark at night. A light blanket is needed, I find the cars to get fairly chilly at night. I think I have also had to use my jacket with the blanket to keep warm.
Instead of a washcloth, I take the moist wipes to freshen up with, you don't have to worry about anything drying. I also take sanitizing wipes to wipe down the sink area, when I am preparing for sleep or getting ready in the morning.
Have a great trip!