I bought into a 1978 C-172N partnership almost a year ago, and was having a
similar problem. I finally figured out that selecting 30 degrees flaps max
until very short final, then bumping it to 40 degrees allows a flatter
approach and much easier landings. My landings have been MUCH better since I
started doing it this way. FWIW, I trim for 85 knots at 1900 RPM when
entering the pattern, select 10 degrees flaps and reduce power to a little
less than 1400 RPM abeam the touchdown point, the speed comes down to 65
knots pretty much all by itself when the 10 degrees goes out. I usually
don't have to touch the trim, just push on the yoke to keep it from
ballooning as the flaps go out. Once the 10 degrees are out, it'll hold 65
with no pressure on the yoke. Then 20 degrees flaps on base, again holding
65 kts. Then select 30 degrees after turning final, then 40 degrees crossing
the fence or thereabouts, slowing from 65 to 60 but no slower until I start
the roundout. See if this doesn't work for you. Your RPM settings might not
be exactly the same as mine, I think our tach is reading a bit low. Good
luck!
Scott Wilson