Can I share a common "Contacts/Calendar" store?

I am a longstanding Windows user who is now "sold" on my iPhone & iPad. I appreciate that I can sync my contacts/calendar between iPhone and my Windows Laptop/Desktops etc. but having my iPhone handy when I login to each Windows device etc. As I have multiple devices, being a retired I.T. type, I would prefer to have a single storage location to which every device I use would synchronize Contacts & Calendar data. Almost all answers to this predicament that I've found so far have a requirement for me to change my EMail address to gmail, or outlook.com or whatever.

So, my predicament:- I wish to login to my very longstanding IMAP Email account and have access to my Contacts & Calendar from whatever Iphone, iPad or Windows device.I happen to be using.

I appreciate that the answer is possibly very straightforward, but please be patient with an old-timer! and please, please, please don't reply with the opening phrase...."If you had a "gmail" email account..... or if you had an "outlook.com" email account. The predicament that I'm in is that I haven't!

Any help very much appreciated. But please type slowly, as I'm getting a bit slow on the uptake!!!

Regards

PS:- I don't need to sync EMail (being IMAP) , only Contacts list & calendar.