One nice alternative to candles-----During the Christmas Holiday Season I always have a lot of the small 'peace light' candles in the windows. I have the ones that work with batteries but even the plug-on type would give the 'romance ambiance' which I think you are looking for on your cruise. Have a great cruise but leave the real candles at home......
No candles Mara. Order a bottle of champagne through the cruise line or your TA. Have it chilled on ice when you arrive. Make up a gift certificate for hubby for a "special" massage at the spa. Many ships now have a couples massage. You could bring along a small flash light and stand it up for some soft lighting or bring a night light. Have a wonderful cruise.
Bon Voyage
Speaking as a ex-sailor, (USNavy), I can tell you that the BIGGEST danger by far of any problem at sea is fire. With that in mind, please, NO OPEN FLAMES.
Jim