Prosites - best way to add a cheaper level

Hi There,
I have a network of around 35 sites, all are paid subscriptions - currently I have 2 levels, Pro (which is the lowest level) and eCommerce (which is the highest) - currently, all my users are on pro as I have disabled the eCommerce option for now.

I want to add a cheaper level to my set up called Basic, however, I'm concerned that adding this in and making it the lowest level will cause issues with my sites on their current level.

For example, my Pro level is Level 1, and eCommerce is Level 2 - if I add a new level (Basic) that will default as level 3 - which would mean my clients on Pro would have to "Upgrade" to that level, which is, in reality a downgrade (as it will offer less). So If I rename level 1 to Basic, level 2 to Pro and add a new level 3 and call that eCommerce, then all my sites that are currently on level 1 will surely be downgraded to "Basic" when their account renews (is this correct?)

My question is, what is the best way to seamlessly add a new, lower level to my set up - I'm happy to manually change things in the DB if this is what needs to be done to make this happen.

P.S. it's worth mentioning that I have a mixture of sites using paypal and stripe gateways - not sure if that complicates things further?