7.1: How to redesign an existing site without template preview?

Hi, folks - about a year ago, I was working on my first Squarespace website redesign for a client. As someone who was/is still more familiar with Wordpress, I was wondering what the best way was to create the new design for my client without (a) messing up their live site and (b) creating lots of complex/duplicative work for myself. In the end, it turns out that working on a new template and redesigning within the "template preview" mode in 7.0 met my & the client's needs just fine. I'm linking the old thread below in case useful for anyone!

However, I'm now working on another redesign project in 7.1. I don't like 7.1! 🙂 In particular, I've noticed that templates are gone -- and with no ability to switch templates, we appear to have lost the ability to use that template preview mode as a staging site. 

So, the question -- how do you redesign a site in 7.1 without affecting a client's live site? Is there anything similar in 7.1 to what 7.0 had, where you could make and preview changes to both design and content in a new template and publish your redesign (as a new template) when it was ready? Have other folks developed workarounds? I know developer mode is also gone in 7.1 now so 🙃🙃🙃🙃 

Any epiphanies in the last 6 months? 😅