if you dont want to go through the hassel of putting on extensions which can damage your hair sometimes and leave you with less hair than you started with you can always tease your hair a little bit and then comb the top to add some volume...or u can use add some volumizing spray to the roots of your hair and blow dry it upwards from the root and use a curling iron to curl it a little bit which will give you tons of volume

GOOD LUCK