Dancing the Morris is usually a performance - you are dancing for an audience. The show can be enhanced by the correct apparel. You may want the whole side to be dressed in a similar manner. Sometimes in the past the dancers wore some kind of disguise either so that they could not be recognised or perhaps as an excuse to look (and act) in a menacing manner. Here are some ideas on clothing;
Handkerchiefs; Typically hankies are white (but this is not a requirement) and are long and billowing so that they can act to emphasise the arm movements of the dancers.
Sticks; Short sticks are usually about 16 inches (40 cm) and long sticks about 24 inches (60 cm) long. Sticks are about 1 inch (2.5 cm) in diameter - about the size of a broom handle. When struck together, the sound should have a slight "ring" to it. In fact, broom handle wood is pretty good. If there is a safety issue with the use of wood, plastic piping can be use. Generally, holding the stick loosely in the hand, but tightly enough that you don't loose your grip when striking another stick, is fine.
Garlands; You can make suitable garlands by pushing tight-fitting wooden dowel or rods of about 6 inches (15 cm) long into each end of a 40 inch (100 cm) long flexible pipe (perhaps hose pipe) bent into a hoop shape. The garland can be decorated with ribbons and real or plastic flowers. A stiff wire can be used to keep the hoop shape if necessary.
Slings; There are many different designs possible but a suitable compromise is to decorate a short length (6 inches, 15 cm) of dowel stick with ribbons with a spray of short lengths of ribbon or decorative ropes at each end. Bells can be attached to the stick to shake in time with the music.
Trousers; Any comfortable trousers can be worn. If you want to be more adventurous, you can wear "whites" (long white trousers) or black breeches with long white socks (plain white football socks are good).
Bells; Most dancers add bells to their costume to enhance the sound of the music. Bells can be strung on thread and hung around the neck, attached to arm bands, or made into bell pads. Bell pads are pads of material (perhaps leather)onto which are stitched rows of ribbons which can "flap" over rows of bells. A strip of material or webbing sewn along the top of the pad and extending from it is used to tie the pads just below the knees and a similar strip, at the bottom of the pad, is fastened around the leg loosely to allow the pads to flap on your leg as you dance.
Shirt; Often, dancers wear a white shirt but this is not a requirement.
Shoes; Often black, shoes need to be comfortable to perform the dance.
Jacket or Baldric; Some dancers wear a tunic or tabard (right) which may be a plain colour perhaps with ribbons attached so that they wave as you dance (above left is a "Forest of Dean Jacket") and some prefer to wear a baldric (top left); two loops of webbing passing over the shoulders and crossing at the middle of your chest and back with a badge or perhaps a rose or other decoration at the crossing points.
Hat; Some sides like to wear a hat or cap. Sometimes these are decorated with real or plastic floral materials.
Your clothing can be modest or as outrageous as you want to make it. As long as you can move comfortably and perform the dance, anything goes.