You can do a sort of quasi conversion with converting just the bunks to rollers but true roller trailers are a different animal with lots and lots of additional rollers. Don't worry, if you only go to one or two boat landing's you will be just fine. Prior to owning a lake house, we'd trailer to lots and lots of lakes and in MN many of the ramps are a joke and the roller trailer takes the worst ramp conditions (steep, shallow, narrow, windy, unmaintained, slippery, descheveled, etc) and makes it seem as though you are on the best ramp it is so vastly superior to my bunk trailers. Most trailers are bunk trailer because of course a roller trailer is more money when you are buying your package when new and people just deal with it and are fine. I can't tell you how many times the bunk trailer folks struggle to launch or retrieve, would see me launch and then comment about it. One of my bunk trailers is quasi converted and it is marginally better.
