I went with a friend who slept on the bed they brought up to our room and he said it was quite comfortable. It may be cooler on the first floor and I don't think the temp diff between April and May would be all that much. The couple I met were not in anyway disappointed with the room. Just mentioned it was warmer upstairs. I know those big fans help. The only thing up there is the bed and bath.
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Sliding to the rail puts you right under the big fan, not shown in pic....stolen from Negril One Stop.

The security at Xtabi is great, you could leave your door open and be just fine...but ask Natasha about it. She is the one who responds to the contact emails from the Xtabi website. She is so nice and accomadating she would let you know if you need more info.