Melt a candle bain marie style set up .... in a pan sat over a pan of boiled water ....... Don't do it with a naked flame going .
Pour it over grease proof paper in a purpose made wooden lipped tray of about 6 x 6 x 1/2 deep, as it cools sprinkle a 1/4 teaspoon of flowers of sulphur over the still soft wax, roll it up reusing the original wick and hey presto you have your sulphur candle . Roll it and trim it so the wick end is flat across the end not pointed .
Unless your respirator is an clean air feed off an air line or is fully self contained one I doubt it will have any safety aspect wrt sulphur gas fumes .
To get over this minor problem
Use a cut down candle say about an inch long stub and poke a hot wire in the base of the stump along side the wick , put the sulphur candle wick in this & sit this new stub on top of the sulphur candle . That way the normal candle wick acts like a lit time fuse and will give you plenty of time to evacuate the green house ..
Remember sulphur burns with an almost invisible blue flame .