I'll second what Brezzin is saying. Bigger is easier because of the reaction time.
I will third it. My first boat was a 33 footer and my father-in-law (a boatbuilder in his own right) said that was a good size because it was more "forgiving".
He was right, for various reasons I don't care to relate...
Having said this, however, I would say the average sailor with average skills who hasn't spent time and money to arrange his lines for single-handing will find 35 feet about the upper limit of comfort without some sort of aids, like autopilot to steer head to wind while you get the main up, or remote control for the anchor so you can drop it from the helm and back down (unless you are good at anchoring under sail, which few are these days).
As for docking, I dock whenever possible in neutral, which I go into from dead slow about five boat lengths before I reach the dock in the old racer and seven lengths and a sharp turn before in the new full keeler, which "coasts" more. I always leave the boat amidships with a line cleated amidships, which I drop on the aft bollard to stop the boat. In my other hand I have a boathook and I tie off the stern line. Then I grab the bow line and the second spring.
If I am encountering unfavourable winds, I will power in and cut speed at the last few seconds with a sharp "S" turn into my slip, which slows me greatly. At all times I attempt to make prop walk and prevailing winds work in my favour. This means I have to THINK about the forces in play and sometimes switch lines to the opposite side of the boat and go in stern first, using prop walk to "get my arse in" or even using a warp.
All this stuff takes practice (preferably against a plastic marker buoy or on an unoccupied sea wall with lots of fenders), but it is simply an extension of what you already know. A very good thing to do first is to motor the new, bigger boat parallel to a wall, go into neutral and see just how far she will "coast" and at what speed you really lose positive rudder control. Next, throw the boat into neutral and do "S" turns...see whether you can come alongside a marker at nearly zero speed.
I found that practice makes, if not perfect, vastly improved. I got to use a mooring for the first time in 2006, and found I liked sailing off it so much that I've started to sail off my dock in the new "clumsy" boat when the breeze is right. It's nice and slow, it's quiet, and most of all, it's seamanlike to handle a boat without an engine.
But I digress...good luck.