Glycerin Suppositories?

i am thinking of taking a glycerine suppository to relive my constipation but what i want to know is which brands are prefered. i have had one a long time ago and it was shaped like a bullet and kind of uncomfortable because it had a point. is there any that are more rounded? do they come in diffrent sizes and if so which ones would be the smallest and most comfortable to get and where to get them? and which ones are big to stay away from?