I very much agree with you that a tiller is the only way to go on a well designed boat between 30 and 35 feet. The difficulty converting from tiller to wheel very much depends on the particular boat. In most cases with wheel steering, there is a set up that allows for a temporary tiller. This setup varies quite widely in terms of layout and effectiveness. In most cases, on a 30 to 35 footer there is an access plate that allows access to the top of the rudder post and the rudder post terminates in a fitting intended to recieve a fitting on the bottom of the emergency tiller.
In the best case, you will need to constuct a simple bushing or bearing at the deck to support a short rudder post extension. At the bottom of this extension post you will need a fitting that will solidly engage the top of the rudder post. At the top of this post you will need a tiller fitting and tiller. In the best case you could probably make the whole thing for a few hundred dollars. In the worst case it could cost thousands. Your best hope is to look for models that offered both tiller and wheel versions because generally these are most easily adapted.