If you are riding dropped handlebars, downtube shifters are surprisingly natural to use, even climbing. Yes, you do have to plan ahead to have some speed and you will lose some of it, No magic. A lot of us think out the shift sequence before we get to a hill. Good derailleurs help a lot (and make a bigger diferfence than on closer spaced FW/cassettes with modern ramped and shaped cogs. (I am willing to bet that once you have tried DT shifters, you will find shifting far more natural than reaching for a stem shifter.)

My all-time favorite shifters for 5-speed set-ups is the SunTour Power Ratchet shifters. SumTour made them in numbers like probably in the 5 or 6 digits and they last forever so finding a good pair is easy. Not hard to clean up and lube. It will work like new when you finish. Use daily. Repeat the servicing every 20 years if needed.

Oops! Talking about being late to the party! (*We got to the address on the invitation but no house! Neighbors said it was torn down 10 years ago."