How much age gap should be given for second baby?

I have three kids. The eldest one is 12, the second is 8 while third is 6. I don't know what the exact or the ideal gap should be, but after having my second ad tried child, I have formed an opinion that if one wants to have more than one child, one should have kids back to back. One year difference is also fine. Because, when you have kids back to back, it is easy, and if there is a long gap, as a woman it is difficult to make up your mind to have more kids after say gap of three or two years because by that time when your life comes back to track that your first kid id little less dependent on you, it takes heart to again get ready to get into the pregnancy mode again.