Is there something wrong with what you have now? Water paramiters ok? Looking for a change?
Personally my opinion is to get rid of crushed coral. If we are talking about adding livesand or liverock then we are talking about natural filtration which occurs with both. Of the choices you list I would get live sand first because if you do the live sand at anytime down the road then it will be easier to do it before you add any more rock.
In a 29 gallon both additions of rock and sand can be done without to much of a monitary burden. You could buy live sand and then add some base rock on the bottom and put your live rock on top of that and let nature take its course.
I still think that a DSB in a 29 gallon is not necessary, doable, but not necessary, a 2 inch bed would do you well IMO.
Just my 2 cents
Thomas
