I personally wouldn't want to do the puppy diaper thing, you would have to give him a bath EVERY day to take out the fecal and urine smell.
If you do use a puppy pad make sure to put a plastic bag underneath it, the so called plastic backing on them suck, and the urine can soak right through..........
Believe me, we have an elderly dog as well
You could also go to a nursing home and ask if they have any old pads that they don't want or see if you can order a few through them. (they have raincoat like material on the back, they put them under the elderly on their beds just in case)
I use these, and just do a quick wash in the morning and everything is all set for the day.