If I restore my iPhone I'll have to get iOS 8.4 I don't want it. But I need to restore my iphone?

Okay if I restore my iPhone I'll get iOS 8.4 which I do not want. So if I restore it and iOS 8.4 is now on my phone, will I be able to downgrade to iOS 8.3? But I need accurate answers. Because if I don't this and I can't downgrade then it'll suck!

Download iOS 8.3 and then restore your iPhone while selecting iOS 8.3. Go on YouTube it's quite simple.