"I simply want to focus on completing the work."
Really, at this point, that's all you need to do. Write. Worry about the formatting later, preferably when you're done. Any writing program you want to use is good, even if it's pen and paper. And if you don't want to worry about how to format, then don't. There are plenty of people out there (and in here) who know how to do it and do it well.
As Melissa said, don't worry about the formatting. It's easy enough to fix at the end. As for programs, our small publishing company has found that MS Word seems to have little to no difficulty in converting/formatting. We haven't used the others.
The only suggestions on formatting/writing in format are:
1. Don't double space between paragraphs, instead use the first line indent function. Indent to 0.25 (If you can't do this, just use a tab. Tabs can't be used in ebook formatting, but they are very easy to eliminate with search/replace and they keep it easy to see your paragraphs as you are writing.)
2. Don't plan on using fancy fonts, they don't show up on ebook readers.
3. Focus on just writing the best book possible. That is the most important thing.
I like your advice and bought a copy of one of your books through your website. It's impressive that you have accomplished so much. Do you have editorial experience as well? I will ultimately be looking for a patient editor, but one who when the manuscript is out there will be ready to help handle the movie scripts and big book offers that will be rolling in.
Life is a suspense movie ~ From Being the Caterpillar