You are right, some of the newer releases you will not be able to get in the eBookwise format, so you'll have to convert other formats if you want to read them. Converting is not exactly straightforward, but it is definitely doable. I've not actually done a conversion of a purchased ebook yet myself--I'm saving that as a reward for finishing all my January writing--but from what I've seen on this board in my short time as an eBookwise owner, the easiest conversion is from the .lit format. I actually just wrote up a post on that process here: <
https://www.mobileread.com/forums/showthread.php?t=68231>.
I really do believe the process is not incredibly difficult, you just need a little patience to get the conversion infrastructure running and to work through the learning curve. Since I haven't done it yet, I can't attest to the process experientially, but I suspect that once all the software is in place and I've tried it for 15 minutes, I'll be able to churn out converted books pretty quickly. In any case, I would suggest looking into .lit conversion first. The other formats seem to have trickier DRM and formatting issues, and there are a lot of books available in .lit.