MN - First - welcome to the forum. Your post interested me because I was in the same boat as you at one time - a lot of us were so DONT be discouraged - the very good news here is if you are seeing lots of deer your doing more good things than I did early on.
Now that being said I must say I thnk a standing shot is a MUCH better way to take a deer for the simple fact that it is a natural shooting position. I always sit with my bow in my lap-arrow nocked AT ALL TIMES NO EXCEPTIONS - Do the same - you will be one step ahead when a buck shows up- as soos as you see ANY buck, slowly stand - and you will be ready, its lots easier to shoot various shots standing....Next advice is to learn to shoot faster .... develop a 'killer instinct' You said you would not shoot a buck headed straight at you - well I would - in fact the deer in my avatar did just that - walked off the trail - headed straight for me and I shot straight down to get him and did it fast...

Learn to draw, aim, release in 2-3 seconds, and PRACTICE it- draw, aim, relax,followthru all while counting out loud "one thousand one, one thousand two, one thousand three......by then the arrow should be gone. Pracitice this at TEN yards, to build confidence in your 'snap shooting' then move on to 20.... This will also help you to concentrate MUCH more which will eliminate the shakes etc...
Next advice - learn to DARF... huh you ask ?
D.A.R.F.-Draw, Aim, Relax,Follow thru.... I think this on every shot - DRAW the bow, AIM (put pin on target-think about opposite shoulder/exit hole), relax (am I rigid, am I torquing the bow), follow thru on my shot- (keep pin on target-dont try to watch the shot) Doing this in combo with a fast shot will help eliminate if not entirely eliminate you over thinking the shot and getting "BUCK FEVER" I never get it any longer until the arrow fllies then I get all shakey and excited !

This is my advice - sorry so long winded but try what I am telling you - it really can help........

Good luck, be safe, and keep us posted.......