Please could someone advise on car seats,currently my DS is 3 and a half and weights just over 15kg and in group 1 car seat. Is there any harm in me moving him to a group 2/3 car seat even though he is not 4 but is the correct weight? I have a problem with my hands and it's such a struggle with the buckle and tightening the straps, and I noticed the next size up you just use the seatbelt which would make a massive difference to me. Don't want to compromise on safety at all so wasn't sure, thanks so much xx