In case you would like to change theme, there are so, so many options… there are sooo many great ones out there I fell in love with…
It all depends on your desired style, your experience, your needs, e.g. you mentioned you would like to have the shop sidebar to appear on the top of the page on mobile devices, etc… what else? amp, bundled plugins, special needs or even apps that come with theme… ?
And on top of it trends and technologies and even needs come and go, what you like today, you might not like in a few years, so it is sooo uneasy to suggest a theme just by asking “I’d be open to changing theme”… you have a fashion website, you might want to build a community in the future or provide advertising, or, or, or… if you are about to change theme, I suggest to consider your needs even beyond the future… 
And there are so many factors that can slow down a website…
And may be you just need to give a little time to the author to make updates after known issues… so it is really not easy to help you based on the details you gave.