Do I need a loft booster?

I've 3 tv's in my house, one downstairs is run off the sky box, and the 2 upstairs are run of ariel points in the rooms.

For some reason we get a rubbish signal upstairs so much so that I have to run the TVs off portable ariels instead.
I bought a digital freeview box in the belief that it would help the signal (as well as getting more channels) but it's worse - I can now only watch any BBC related channels.

I'm not very DIY minded - I've seen a small white box on what looks like the ariel cable in the loft, and I've heard about loft boosters but not really sure if that's what I need?

Grateful for any help, Advice

Little Jo
October 2008