Best dog type for ........?

I live in Ireland which has weather that is not to extreme .I have a small back garden (roughly 6 meters by 6 meters ) but i live near 2 large public parks and have no problem walking the dog more the 3 times a day :) there will always be someone to look after the dog as my mam does not work and is home most of the time . i will be able to come home from school every day at 1 o clock to give the dog a walk for appox. 30 mins then im back to school for another 2 hours . My mam CANNOT walk larger dogs as she is not that strong to walk larger breeds but the rest of the family is . my back garden has a well shaded area and enough space for him/her to walk about . Any ideas of what type dog i should get ? i would prefer a larger breed e.g. boxer etc. ?:)