Hi Jennifer,
According to your description, I suggest you stay using Enterprise plans because the Skype for Business feature you wanted is just for Enterprise users. For this feature, there is not an exact date on official resources when it will be available except for Enterprise users. You may consider sending your feedback on this feature to our related team via this link: g.microsoftonline.com/.../135.
If you can accept the situation above, you can buy these subscription Business Premium and Business Essentials within your current tenant in Purchase Services page. Then, assign the newly purchased licenses to the users, and cancel the original Enterprise plans.
Best regards,
April Zhou