Just because your IUIs were not successful does not mean IVF will not be. Plus, this next IUI very well could be successful.
You have a pretty good antral follicle count. Your FSH is not that bad. There is no reason to think this cannot work for you. Most docs who are up to date with the literature say FSH is not a reflection of quality, but quantity. You quality should coorelate with your age. At 38, it may just take several tries to find that good quality egg. It isn't that they aren't there, just that we need to try a little more.
I also have a child (2 years old). I conceived her after 2 years of trying with an FSH of 18. I am trying again and my FSH is 32 (I am 35). I have consulted with Dr. Davis at Cornell who says I have a 30% chance of success with one IVF. Your FSH is better than mine, so I would say your chances are at least as good as mine.
Also, do not be swayed from being on this board because you have a child. There are people on here that have children. When you post, just mention it in the title if you are talking about your child. I have found this board to be more active than the secondary infertility board.