I'm a designer specialized in websites and print and I have a passion for publishing and illustrating. I would like to make a career change. What do you think would be best profitable: launching an illustrating activity or an ebook publishing activity?

I would start by working on the new things on the side. It's possible you are just looking for an escape from your current work and perhaps you're not sure yet. Perhaps you can reduce your hours at the current job down to 3 or 4 days per week and then work on the illustration for 1-2 days per week and perhaps on the weekend. Going freelance or building your own business takes time, lots of it. The eBook isn't as lucrative as you might think (at least not with a bit of work beforehand). eBooks don't sell themselves, you have to constantly market them. My suggestion would be to start the illustrating activity slowly, create a brand of your work, do it on the side and see if it's really what you want to do. Doing so as a freelancer or bootstrapped startup takes time, you will have to deal with finances, administration, getting clients and so on. Once you have a brand and you have quite a few people reading / learning your stuff, you can start writing & selling the eBook, because you will already have readers who are interested in your work. A simple way to start up the branding is perhaps to start a blog (and write regularly) and offer a newsletter. The newsletter will then be a good way to get people to come back again and also a channel to sell your eBook to the interested readers. Just writing an eBook and hoping people will constantly buy it while you lay back will NOT work.

Develop your portfolio!  Improve ur skillset. Takeup projects quoting too low, build client base, talk to people with similar interest, freelance or get in touch with online professionals. Then go for projects on your own.