I'm sure this has been done before but I can't find it, so apologies. DS is not quite 6 months and has just about grown out of Primo Viaggio car seat. He can't sit up unaided, isn't quite 9 kgs and I don't want him front facing anyway until he is a good few months older, so he can't go into DD's old Renaissance. We tried the Britax First Class which goes both ways when we first got a seat but the inept guy in Halfords couldn't get it to fit. I will try somewhere else and have another go with someone who knows what they are doing, but if it doesn't fit has anyone got any ideas about something else I could look at ? Many thanks