Moving back to the U.K

Can you Please help? Am Planing to move back to the U.K around December/Januaury time, from Rhodes Greece & will have too much for the plane trip, as i have 2 cats to take back, I wont have any furniture, more like my dvd's clothes,bric- brac stuff, as yet am not sure how big the box's will be or the weight, but feel that i will have 3 box's in all, I will be moving back to Southampton, (even Portsmouth is a good pick up point for me) As you can tell I've never done this before so would be grateful for any help, on picking the right box sizes and cost, I don't mind my things going before this time as my Brother would be able to collect my things in the U.K for me. Many thanks Anne Dickson