The sports complex thing sounds fun. You could do a bowling match; girls vs boys for example. For the bowling thing, you'll probably not even need your parents there because there would be so many of your friends and mates there that they'll never have time alone with you. So after a long day bowling and maybe indoor skating, you could then relax and have your sleepover.
Im thinking of getting a bouncy castle and inviting my whole year to come (which isnt much, very small school) then hire out a local sports complex and have the bouncy castle there, seeing as my birthdays in March and will probably be raining! Then buy a load of frozen pizzas and chips and have that for food :) And of course, sweets and cake too! And invite my closest friends back to mine for a sleepover:) Whatcha think? Either that, or paint balling, but Im pretty sure that'll work out more expensive! Also, I was thinking, would my parents need to be there? Like I dont mind them being there, my parents are pretty cool but it'd be nice to be alone with all my pals, do you think other parents would see it as an issue seeing as theres gonna be a bouncy castle?