Maybe you can make some friends at the local lgbtq groups. Then you can go shopping together, which feels a lot safer.
Also this sounds weird but it might be easier to go to a female only store. That gets rid of any unclarity for everyone involved.
You might just pay a visit first and see how the employees react. Maybe talk shortly with them and ask them when it’ll be the least busy. Maybe browse a bit. Also some stores have more hidden changing rooms than others, and mostly you’ll be inside any way. Especially if you have someone to help you. Again you can ask an employee for help to here.
As I mentioned somewhere else, you’ll notice quickly if you’re welcome or not, and that’ll depend on your local culture I imagine. I’m from a conservative area but have had a lot of support. You’re dealing with people who are into fashion any way.