Hello & welcome to A Gardener's Forum.
I looked this up for you and here is what I found:
repotting is best done in the spring
All of that preparation to make a well draining soil is not necessary. From what I read, Peace Lilies are not fussy and will grow well in almost all well draining potting soils. So, you could just buy a good potting soil.
If you are concerned, you could add some peat moss (it is sold with just that name in bags) to a regular potting soil that you have bought or if you have some sand you could add that to the potting soil mixture instead of peat moss.
I would think that a ratio of 1/4 peat moss or sand to 3/4 potting soil, or if you like 1/3 peat moss or sand to 2/3 potting soil would work well. You are just trying to make a better draining (looser) soil...Mix the 2 together well.
Choose a pot that is one size larger.
(ex: is if the existing pot is 6 inches wide, then you should chose a pot that is 7 or 8 inches wide.
The pot can be made out of any material, but MUST have drain holes. If you would like, you can cover the drain hole/s with a coffee filter or a paper towel to prevent the dirt in the pot from washing out of the drain holes.
Place the old pot on its side, & lift the pot from the plant. Inspect the root system. Healthy roots are white or light colored. You can cut off any dark, black, soft or offensive smelling roots. Next loosen up the roots, esp. those that are going around the dirt in a circle.
Put a bit of soil in the bottom of the pot first, then add the lily
and fill in the area between the existing lily
ball and the new pot. firm down the dirt. When you are done, the top of the old dirt ball (where the lily
meets the old soil) should be 1 inch from the top of the new pot.
Water in the lily
until you see water running out of the drain holes.
Place plant in a area with indirect light and water only when the soil feels dry to the touch.
I hope this helps.