I know it sounds odd, but go to a beauty salon and have them dyed. I find apart from colouring them it also bulks them out a bit more. Go for blue black - sounds horrendous but is actually just the darkest tint there is. The added bonus is that you can be makeup free and still look fab! I swear by doing this regularly and by mixing in fake tan with my evening moisturiser. No need for mascara and foundation during the day now!
Another thing you could try is the new type of fake lashes where instead of a line of them you put single ones on at a time where you need them My aunt loves them, and they are easier to do and far more natural looking.