The IVmaj - Imin is not a bad progression if you have the right melody in mind. Actually I think it has a nice exotic flavor to it. If the 6th in the melody occurs on a harmonic beat and then resolves to the seventh as a passing tone. The IVmaj is a solid choice for harmony, or at least the basic foundation for it.

In melody writting in minor, I think the melodic minor is perfect. The leading tone and although it occurs in the harmonic minor scale. The third between the the 6th and 7th is wrong. The way the melodic minor fixes this, and even the rules on it's usage is still correct to my ears. I rarely ever break the guidelines with the melodic minor scale.