Go to your local Sherwin Williams store and buy either a foam roller
cover or a mohair cover. They'll know what your looking for. Also, to
help with leveling, buy some Penetrol. Add about 1/2 cup - 1 cup per
gallon. This will help tremendously with brush marks. If you still
have problems, it could be the primer underneath. It you don't start
off with a smooth surface, the best paint in the world cannot fix it.