Proof-Reading Solutions

Typos and errors are the bane of any publisher, not just the SP crowd. Last I checked, a Traditional Publishers would keep a typo log so if a book had a second print run the typo would be fixed.

The thing about Word , red and green underlines aren't always mistakes. You have to add words to a dictionary which is limited right out of the box. And what it highlights on grammar may be accepted usage.

Being a bit of an unusual case, I edit / proofread my own work. Write it, let it cool down in my mind for at least a few weeks, go in and hunt bugs, then do the same wait and hunt cycle. I rarely ever share a raw rough draft with anyone, because I know the work isn't ready and it is indeed rough. I like to find all [or the vast majority] of the "ticks", "fleas", and "nits" knowing that there will always be one or two more to find after 60K, 70K, or 100K words; it's inevitable.

Like a Trad publisher, I can get that manuscript pretty squeaky clean, and a year later find one word or one bit of punctuation to fix, perhaps an extra space to remove. Paid proofreaders do make mistakes as in something slips past, because I've got more than a few Traditionally Published books by famous authors where there's an odd typo or two. I've read work by an unpublished author, in the 250K word range without any typos or errors I or someone who is good at proofing work could find. That writer is pretty much a perfectionist.

Basically put, with the steps you're taking you're already doing due diligence, and other than paying people [which can get expensive in a hurry] with the realization that they're usually not going to be 125% perfect, either keep a revision log or do the odd revision when you must.

My rule of thumb is if you have a fairly long MS and can get the typos under five the first time out you're doing pretty good.

Perfection is an ideal few if any will ever attain, but getting really close to it is an accomplishment.

Actually I'm not blind to my mistakes as I'm very aware I make them, but I also realize due to personal context [disabled spouse, three small children, other things to do as well] it's better to get the writing done while doing my best to not make any mistakes along the way [which is virtually impossible when one has to keep bouncing up to take care of something].

After the work has cooled down in my mind for at least several weeks, I make my first editing pass and it's like looking at someone else's work. Second pass is the same thing.

Put it into perspective, if you have only 5 typos in a 170K MS, that's an error rate of 0.0029412% and that's good.

I would suggest using a human copy editor/proofreader rather than depending on software (especially when it comes to grammar).

The importance of an independent, objective reader cannot be overemphasized because, as you say yourself, it is too easy to "become blind to our mistakes."

Spellcheck et al are fine for the first pass while writing, but these have the all-too-obvious drawback of not being able to identify homophones. So you could easily wind up with "sale the boat" instead of "sail the boat."

naturalreader.com doesn't sound like too bad an idea, though I suspect that it would have the same problem with homophones. But...reading your work out loud yourself is an excellent idea. For one thing, it forces you to look at every word where there is always the danger when reading silently to see what you think you wrote rather than what you actually did.

Professional publishers divide the work up among different levels.

The first is the editor, who is responsible for the overall sense and structure of the book.
Next is the copy-editor, who is responsible for the book's grammar, punctuation, spelling, syntax, etc. Often the job of the editor and copy-editor will overlap. This step in the book's editing process may have numerous iterations, with the MS going back and forth between the author and the editors until it is deemed finished. (Editors do not themselves make changes to books. They only indicate where changes and corrections need to be made. It is the author's responsibility to implement them.)
Finally, there is the proofreader who checks the final version of the book against all of the changes that were supposed to have been made, and also double-checks to make sure there were no overlooked mistakes.

Even after all of this, errors will still slip in, but as sphinx-cameron pointed out, they are usually very small in number in proportion to the size of the book.

Thanks for the advice.

I have obviously thought about the traditional route, and I am still open to it. There are a few reasons right now why self publishing suits me:

1. I am a bit of a maverick by nature and do things my own way
2. For my subject matter I have actually built up quite a stable and modest following, but proper advertising would obviously help
3. My last book was judged successful (in terms of reviews) but it did straddle a dangerous ground between academic and popular. I knew this approach would work, but I can imagine the book fitted into a sort of no-man's land for that reason.
4. I once wasted a long time formatting a book for a publisher, but never heard from them again, so it put me off the whole proceses. 

Many thanks for the advice, though