I would like to see some steering wheel conversion pictures on the O'day 25 or a similar sized boat, and get some ideas/feedback. The tiller seems to take up too much room in the cockpit, especially when you have 3 or 4 people on board.
If you're thinking about a destroyer-type wheel, my 2¢ is don't do it. A wheel like that on a small boat is just silly. A "forward-facing" sorta wheel, like the old Edson steering mechanisms (see below), is slightly more sensible. However, on a small boat a tiller really is the best way to go. Small boats are inherently "squirrelly", so you need to react quickly AND have the tactile feedback only a tiller can give you. The only reason to switch to a wheel is for the mechanical advantage, which you really shouldn't need in a small boat.
There are ways to work with an autopilot and extend the tiller to the rear that will let u flip up the tiller and buy more space in the cockpit under autopilot. I have seen pictures but have no idea how well it would work for you.
I have sailed on an O'Day 25'. There is no way I would recommend putting wheel steering on a boat like that.
If you find that the tiller gets in the way in the cockpit then change the tiller shape. Much cheaper, simpler and expedient. Choose a tiller shape that rises up ('S' shape, sort of) and will float above the knees of your guests in the cockpit.
To convert your boat to a wheel, with new parts will cost over $2K + labor. With used parts around $1K + labor. Then you'd have a steering mechanism that would give you no feedback, and is much more complicated (and prone to failure) then what you now have.
Your boat, your money, your choices.
My boat: Tartan 27' with tiller steering. The tiller can be raised once at anchor making the whole cockpit guest friendly. Not so with a wheel which usually takes up more room than a tiller in any case.
I'll second everything Caleb said, and mention the additional advantage of a tiller letting the skipper steer with his/her feet/legs/butt while using both hands to untangle a heap of line, or keep a chart semi-flat and readable, or opening a beer, or wiping your four-year-old's nose (or whatever else needs wiping at that moment). Try THAT whilst steering with a wheel.
Thank you all, good information here. A deeper "S" shaped tiller is probably the best answer. I wonder if they make one with multiple pivots so you can change the curvature of the tiller to fit your circumstance.
Take an already space-challenged floorplan and shortening it even more? . Only way I'd change out the tiller would be a direct-coupled, gear drive, 1:1 wheel mounted on the useless real estate directly above the rudder post. BUt then, I'd need to swap out the end-boom sheets and add a traveler sommere's else with al the associated hardware.