Step 2 - Marking how much wider the top is (ie the angles of the sides)

1) Mark a ruler / stick / pencil at the depth of the mattress that you want

    (e.g. 7" for most pocket sprung mattresses)

2) Hold the stick / ruler vertically on the edge of the template and using a tape measure note the distance to the side of the hull.

3) Write this distance down on the template and repeat at the corners and two or three places along each side.

How to make a template?

Step 1 - Make the mattress base template

1) Lay a large piece of brown paper on the bed base.

2) Crease it by running your fingers around the edge.

3) Cut this template out. And check that it still fits the     bed base nice and snug. - Adjust by adding or     taking away off cuts