Originally Posted by Germany_chris

Why not a subcompact double 44/28 or 42/26

The rear derailleur cage is long so replace the cassette w/11-34 or 11/36

Originally Posted by shelbyfv

That 9 speed RD, even though a GS, won't take more than +/-27. BITD we replaced them with MTB RDs to use a 32 or 34.

Originally Posted by KCT1986

Please post a picture of the shifter or the model number.
Model number of Shimano shifters are located here,

Originally Posted by Bill Kapaun

42/23 = 1.83 is your current lowest gear ratio.
34/23= 1.48 Gear ratio by changing smallest ring and using current cassette.
42/28= 1.50 Gear ratio by using a 28T largest cogged cassette and NOT changing small ring.

Get a cassette with a 28T largest cog.
It'll give you almost the same lowest gear and is the simplest solution.
Your chain might need to be lengthened 1 inch. Maybe 2?

https://www.amazon.com/Shimano-Casse...g-goods&sr=1-2