My boat sits on bunks. I found steep slips best as I could launch without getting the rear of the van wet. Anything that wasn't steep needed an extender bar.
I bought one that comes in 1m sections (4 in all). Found that was all I needed in the end. Oh, and someone to ensure it stays straight when I reverse.
I did consider modifying the trailer / bunks and looked at all sorts of rollers, set ups etc. Also talked in depth to a trailer manufacturer.
In the end the cost of modifying everything compared to an extender was not worth it.
Having said all that now I just get it craned in/out