Apple Watch and O2 contract

Hi,

I've been on O2 with a prepaid number for around 4 years now, and have been very happy with the service in Berlin and the price.

I'm wanting to add an Apple Watch with cellular to my account. Thanks to the very helpful O2.de twitter team 😀, I now understand that I can't add a cellular Apple Watch to my prepaid account (which is quite a shame 😞 ).

So, my question is what would be the best way to do this? I currently use no more than 2 GB of data per month in total, and very few talking minutes and SMS's (probably less that 30 minutes and 10 SMS's). What O2 offering would be best for my iPhone (nano SIM) and Apple Watch (eSIM) based on that, and how much would it cost? (I expect the Apple Watch data usage to be very low.) I'll be honest, if it's much more than I currently pay (less than €15) then it's quite unlikely I would even consider it!

Thanks!