Recommended dock line

I am in need of a dockline for my 19 ft ProGator bassboat (150hp Mercury). It's a heavy boat. I am thinking floating dockline is best because this is for launching the boat and if it floats, the line is less apt to get tangled into the back of the trailer. Wondering about length.

Here's how I launch. I unhook everything and then back the trailer into the water, and with a rope attached to the bow, I can then very slowly pull the truck n trailer up such that the boat will then follow me. Two good things could happen. First, depending on the ramp, if there is a dock, I can just walk back, untie or unloop the end of the rope affixed to the hitch end of my trailer and walk over to the dock and tie the boat down and go park my truck. Or, if there is no dock, I hope that the boat curves just a tad when it floats away from the trailer and then I can give a little pull with the truck and get it aimed for the lake bank away from the concrete launch so it doesn't skin up the keel of my boat. Either way, a rope with a manufacture loop end if helpful. Those woven loops are permanent!

Does anyone think that a 1/4 inch dockline would suffice for this? I have used 1/2 inch and that's plenty big but I'm wondering if smaller will work because it seems the right length is a bit difficult to find and with everything I buy for the boat, bulk and weight are always reduced where I can. It's not like this rope would have much pull on it but I sometimes I fish a river and it has a good current, so, watching the boat go byebye downriver would not be pleasant.

EDIT:  Found this link after a ridiculously long search for floating dockline. It seems that 3/8 inch or larger would do. I don't know if all of this floats or not... info for docklines. Another thing is finding desired length. My trailer is about 21 ft long, and I figure about ten feet longer is needed so that when I pull up the truck, I (hopefully) will not need to wade into the water. So, 30-35 ft long rope seems right.