Slippery Pete and Sunfish have the basic story ...
majority of my landings have been ballooning and if not, then they have been really hard landings
Suggests that you are maintaining concentration on the aiming point for too long and then flaring by guesswork .. which doesn't work very well
getting the seat height just right
Absolutely .. and quite important for IFR low vis landings if you progress down that street. Suggest you move fore/aft so that the legs and arms are comfortable on the controls and then up so that your line of sight runs down the top of the glareshield
(a) get the trim set for the final speed by, say, 300 ft so you don't have to fight the elevator loads while you are busy doing other things
(b) maintain the pitch attitude and, subject to turbulence, you should find the airspeed reasonably stable
(c) drive the aircraft down to whatever is your aiming point. This is much easier if you have a physical reference on the ground .. eg runway or runway edge markings etc
(d) at some height which you will eventually settle on for yourself .. and which will vary with crosswind particularly .. flick your eye focus to well down the runway so that you are, in effect, looking near parallel to the runway surface. I'd go for around 20 ft or so initially and then ramp it down to, say, 10 ft .. if you do this transition too high you are likely only to confuse yourself and, more dangerously, end up floating excessively.
(e) peripheral vison cues will allow you to sense the rate of closure with the runway surface. Eventually you will "get" the picture which should be associated with a gentle flare.
(f) the aim should be to flare so that your wheels are just off the runway and then let the aircraft settle without tolerating more than a short float.
(g) excess speed is a real trap for young players. Have a look at the POH recommended speed and ask yourself why you are flying faster if that is relevant ?
It takes a while but keep at it and it will come together.
Another idea to minimise all those things which are distracting you with multiple sensory inputs is to talk your instructor into a session of circuits with a nice big high sitting over the aerodrome and right on dawn .. best chance to get nil wind and stable air. This allows you to see the important bits rather than getting tangled up with the distractors.
Also, if you have the approach reasonably down pat, get your instructor to do the final bit of the approach/flare/touchdown and patter you through what he/she is doing and thinking for a couple of landings ... that should help you get a reasonable mental picture of the desired spot to flare without too much lost time.
And .. don't sweat it too much ... even the aces get the odd surprise from time to time. Mind you, when I went onto the 722, my first block was with a lovely English greybeard gentleman who painted it on every landing without fail .. in some contradistinction to my own efforts at the time. Actually, with that model (which had a reputation for difficult landings) I got on top of my problems when I gave all the guidance the flick and just landed it like a 150 .. my landings went from generally dreadful to generally nice with the occasional greaser.