Well, all pajamas are flame-resistant. You won’t need to worry about pajamas. When the baby is asleep he/she is not in harms way.
Even though is shrinks, you should get mostly cotton in your baby’s clothing. Cotton is treated to meet flame-retardant standards. You don’t need to worry that much about shrinking, because babies are constantly growing, and the clothes won’t last long anyway. You may have to get one size larger to fit the baby’s needs.