Should i host my Coming Soon Page in subdomain o in my current main domain

I am currently redesigning the website of my software development agency and I built a very complete coming soon page (with information about what we do, our social networks and a form that when you register your email offers you a unique discount code that we will use for a promotional campaign, plus emails for marketing thanks to that form).

My question is, should I set up the coming soon page on a subdomain (next.yourdomain.com) or should I set the current page I want to change as (old.yourdomain.com)? Mostly I don't get many visits to the main site so it's not that much traffic right now and in the coming soon I put a link to what would be the old site in case someone wants to see the projects that were there.

Thank you very much, I know it can vary a lot the results but I am sure that the coming soon will attract much more visits than the current site thanks to the promotions campaign.