If you aren't that great at holding the floor, maybe it would help to find a way of dealing with your ds's debating that doesn't require you to hold the floor
.
One way that comes to mind is if you said your one or two sentences, and then let him have a one-sided debate, with you listening but not responding beyond standard "I'm listening" noises and body language, let him have his say for either as long as he wants or for a specified time (maybe set a timer), and at the end of it give a brief recap of his points, say you will consider it and give him an answer later (perhaps at a defined time, like the next morning), and then do just that. Consider his ideas on your own, at leisure, and then tell him what you decide in just a few sentences.
And if he wants to debate, you can repeat the above process till either he gets tired or you decide to put a stop to it, declaring this decision closed.
In any case, you can let him have his say without engaging him in debate, if you don't want to - if you do better listening and thinking before saying a little, then go right ahead and do just that
. Just because he wants an answer Right Now doesn't mean you have to figure one out right now, if that doesn't suit you - it's perfectly valid to listen and tell him you will think about it and decide later
.
Any of that help?