Try the link below. Enter your own city and likely there will be hundreds of volunteer opportunities and you might find one that fits the bill for YOU.http://www.volunteermatch.org/
First let me say we find the same issues you mention but after ten yrs retired I haven't become bored like my spouse. But mostly we find things such as a ride in the slow traffic times like Sunday morning and we ride and see dozens and dozens of horse ranches. We found a Saturday market for fresh goods with 75-100 vendors about 50 miles away. We travel there and lunch somewhere different on the way back. We walk about 2-3 miles 5 days a week. Work in our 1/2 acre private back yard with flowers, shrubs, etc. Read, cook, etc.
I've come to understand my spouse feelings that something different is needed very often. So every few hours we might watch something on tv for several hours, or the computer, or the yard...but we change every few hours. And we seek somewhere to go once or twice a week within a few hours drive for half to three quarters of the day.
I mention these examples to entice you to give the link a try. Also spend some serious time thinking about what you enjoy and seek those directions along with others to spread your time. Remember when you worked all those hours on serious business..well spend some focused time with this project and you might be surprised.
A neighbor has volunteered for 11 yrs at a local non-profit live theatre next to our local museum. They have plays about every six weeks. While one play is performing in the evening he and about 4 other volunteers work during the day with one paid staff building the stage sets for the next play. They have more professional building equip in one place than I've ever seen. Now that isn't my cup of tea but I was so surprised and the size of the "back-room" operation when I worked with him.
Last year at the link above I found a non-profit international wild life park about a hundred miles away building a new park in my area to relocate their wild animals. They needed help at the new location for about a year.
We are not so much into socializing so we need to find other avenues to occupy our time. If you enjoy socializing then try a few local clubs, like mentioned above, for card games, etc. Also found a County library volunteer position just three miles from me.