I just use a little, LITTLE bit of whatever product I'm using (unless I'm like month's past my last relaxer then it's just going up in a bun anyway). For any cream based moisturizers like phyto 7 or 9 you want to use a very small amount and then rub that all over your hands and fingers then distribute it evenly through your strands.
I know some have used dove's light moisturizer and that was tricky for me cause sometimes the "spray" comes out more like a squirt.
But if you spritz it right (far enough away from your hair for the mist to hit it and not an overly powerful spray) you won't weigh your hair down as much.
You might also want to alternate adding products to every other day if you find adding stuff daily weighs your hair down.
Oh! Also, try to steer towards products designed for fine hair especially so close post relaxer.
I would never use shea butter on my hair (and even very far post it's a bit heavy) early on because I know it's too much at first! You can gradually increase the "heaviness" of your products the further out you get from your relaxer day.
You can dilute your leave in with a little water to make it lighter on the hair as well.