Guys, 1x is not the solution for every situation! Especially true when addressing riders loosing power due to age or other circumstances.
He currently runs 26-36 (roughly 19 gear inches) and is asking for a combo giving him something lower. The 1x advice presented above is 23.8 gear inches. Huh? Just get off and walk?
The way forward from here is finding a long cage rear derailleur capable of the most chain wrap. Once that number is established start looking at the cassette/chainring combo that gives both a deep gear and reasonable top end speed.