As with others, assuming you have stock tires (or even if you don't), and proper air pressure in 'em, a 122 should steer quite lightly.

Steering box too tight a definite possibility. Does the steering return to center as it should? If not, I'd be looking into a problem and doing so fast. worn or dry lower ball joints can cause stiff steering, and thats no something you want to have break. Been there, done that. It sucks.
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-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC

A smaller wheel would give you less leverage and therefore require more effort.

Question is, though, why does it take much effort? I don't find out 122 takes much muscle at all, even with fat tires -- wife is having therapy for shoulder problems that limit what she can do, and she has no trouble driving it even with that. Of course everything's relative and it's not as easy as our 245 with power steering, but not night and day different either.

I just corrected a really stiff 122 that turned out to be nothing but an overtightened steering gearbox. Too much caster might also make it heavy at low speeds. Aged/failing ball joints can get very stiff, and are also dangerous.

Suggestion: Put the front of the car on jackstands. You should be able to spin the wheel with just about no effort. If not, there's a problem. If so, you know the gearbox isn't dragging.

Next jack up the lower control arm on one side so it barely lifts the car off that jackstand. Try the wheel again. Repeat for the other side. If it gets at all stiffer, you have ball joint problems.

If all that is good and it still drives stiff, that suggests alignment. If the car really fights turning and the wheel spins violently back to straight if you release it, that's excess caster. You do want enough caster so it self-straightens, but not so much that it fights you.

My guess is just the opposite. A smaller steering wheel would make it harder to steer. Think you could find a larger one? :)
DC