I haven’t read all of the replies on this thread, so forgive me if I repeat some advice. If you know how your mother and sister are, is it worth it to have a chat with them before hand about how they made you feel at the bridal show, and how you would appreciate behavior X instead? Ultimately, you teach people how to treat you, and it sounds like they either are not aware of your personal boundary structure, or don’t care. There has to be some kind of feedback for them, however, if you haven’t established healthy boundaries. This is only if you choose to have them along in choosing dresses.
Keep in mind, though, that there is absolutely nothing wrong with going to try on dresses alone. Do you take people along with you every single time you buy a garment? Of course not. It’s kind of a shame the bridal industry has built up mundane tasks as “events,” because when people like you and I try on dresses, it’s another thing to feel terrible about when we don’t fit into a neatly packaged norm. For the majority of my dress appointments, I was solo also. Yes, it sucked at first, because my mind was hung up in “should-ville,” thinking of all the things that “should” be going on in my life that were not, and was not going to change. My mother shows me love in other substantive ways, and I needed to appreciate and respect that. She’s not one to go celebrating things like this in my life because of things limiting hers, and that’s ok. At the time I was getting married, my sister’s marriage was falling apart, and she was less than excited to be celebrating matrimony, so that was also a no-go. I didn’t know that at the time, but in retrospect, I understand and empathize why she didn’t join me with bells on.
And to be absolutely honest with you, I felt less encumbered during my trials when I was by myself. When I had a couple of bridesmaids with me, I felt more pressure to please them rather than me, which was weird. Also, after a time, I could see boredom on their faces after the 3rd or 4th dress, and that made me feel self conscious and like I had to speed things along and make a choice to get out of the store faster. You don’t want that. Go at your own pace, look at dresses *you* want to look at, have reasonable communication with your dress consultant and ask as many questions as you can. Really, you’re just buying something that you’ll wear for 5 hours, tops, and never wear again. It’s the marriage you should putting your stock in, not the dress buying. The only two people that matter are you and your fiance, so try to focus on that aspect of your future. I promise you will be happier for it.