You have a lot of good advice as I scanned over what was here so I'll try not to get redundant.
All 3 of my children were complete surprises and each a blessing. First, I've never actually heard of choosing the gender, but if it's possible, then I'd do it holistically. I am very much against drugs (legal or otherwise) and there are some things that popping a pill cannot help.
Secondly, you know what you went thru when you had your other children, the stress on your body, all the changes, and don't forget about labor! That in and of itself can send some women running into the OR for a tubal ligation. I have 3 children, my 2 boys are 18 mo apart and the third came when I was in the middle of my divorce (talk about stress!) and so there is a 6 year difference with my younger son and daughter but I found that having my boys close was pretty good because they grew up together and weigh wise, I wasn't quite back to where I wanted to be, but then I had the chance to lose it all at once.
The bottom line is this: if you think you are ready, then go for it. If not, then explain to your hubby that you aren't ready yet and you'd like a bit more down time. My boys were terrific with my daughter and extremely protective of her, too, so your boys might react the same way if you wait, too. I'm not saying it'll happen, but it could.
In the end, the decision is yours and does not necessarily even need to include your husband (not what I would do) but you know your body and what you can and cannot handle. I wish you the very best of luck in your quest and with your family. If I can be of further assistance, please reach out to me...good luck!