Hi there,
In what format is your current eBook? Is it in PDF format? Also do you have the source files?
Regarding ePub and Mobi, there are eBook two formats:
1) Fixed layout: It looks just like a PDF file but in ePub/Mobi format
2) Reflowable layout: The content (text, images, page size) can be scaled to fit any screen.
The process of creating each of these is different but InDesign can generate both (not directly the Mobi though), the norm for ePub/Mobi is reflowable layout but since you can't create complex layout, many creators opt for fixed layout.
Feel free to contact me and we can talk more.
Please do have a look at some of my other eBooks here:
https://www.freelancer.com/u/Marzia87
Thank you for considering my proposal,
Marzi