Best Way To Upgrade Plan To Allow For Simultaneous Editing

I’m getting conflicting information about the best way to add a new user on my current starter workspace account. Originally I assumed I could simply upgrade to a core plan, as that is listed on webflow’s pricing page as allowing for 3 seats:

But when I try to upgrade my workspace plan, I’m given this pricing sheet:

Which suggests that I have to pay $120 a month on top of the site plan to simply add another editor, despite what all other webflow pricing information states about workspace plan seats. I’m aware that I can add a freelancer account too, which I’m considering doing instead, but I want all users to have simultaneous editing capabilities, and it’s not clear whether or not this is allowed with guest invites. I don’t need simultaneous editing for more than a month, so I’m looking for a temporary option here, but this pricing plan is truly indecipherable.