A lightweight t shirt or tank top are fine as are leggings or even skinny jeans. Its even more important to take your own body measurements for sewing clothes.

3 Ways To Take Clothing Measurements Wikihow
Take body measurement for clothing. Many clothing catalogs or fitness programs ask you to take body measurements. Even if your body measurements dont match exactly one of the pattern sizes fewer adjustments will be needed if you get the correct size. This will ensure a more precise fit. Most clothing lines use the measurement of the natural waist for their size guides. Take your time to read our tips first. All you really need is a soft measuring tape or a piece of string and a regular tape measure and preferably someone to help you though you can do it yourself.
Given your asymmetrical body shape you will be asked to take the measurements of both limb circumference. How to take body measurements for perfect fit. This measurement is used for tops dresses and bottoms. Taking accurate body measurements is one of the keys to great fit. And a well fitting block is critical to the success of everything you make. One of the first steps in sewing clothes is selecting the right pattern size.
Beneath your clothes different undergarments will result in different body measurements. A guide to taking measurements for a mens suit. To measure your natural waist you want to find the narrowest part of your waist located above your belly button and below your rib cage. Below is a full list of the 12 essential measurements and 5 build data that our tailors need to know. Note some brands use a low waist measurement. Whether you choose to make your pattern block from a commercial fitting pattern or draft it from measurements having accurate measurements is critical to the success of your block.
While you can take measurements against bare skin you can choose to slip on a thin layer of clothing.