A 6m old is nowhere near developed enough to ride ffing in a car - there is a new law coming in later this year (Europe wide) that will ban ffing for babies under 15m. That law is generally considered a step in the right direction but not far enough as rfing to 4y+ is the safest way for a baby/small child to travel.
Legs over the end of the seat is find - DD4's legs are bearing the edge of her Britax Baby Safe SHR II and she's 11lb & 15w so she is really NOWHERE near being ready to ff! DD3 is 3y 3m 15kg & 94cm (IIRC!) and is rfing happily in a Britax Hi-Way II and DD1 & DD2 both rf to ~4y+ in a Britax Two Way Elite. DD2 is ffing in the TWE & is 19kg & ~116cm as it can be used ffing to 25kg with a harness.
If your baby is looking snug in their car seat, check the manual to make sure there isn't any padding/insert that could be removed to make it more suitable for a bigger baby as some seats have newborn inserts to pad out the interior to make it smaller for a little baby.
Also baby shouldn't be in a padded/thick coat even in winter as the padding can stop the harness from restraining baby in a crash - thin layers & lots of blankets over the harness as needed or a cosy toes made by the car seat manufacturer to fit that model (e.g. a Maxi Cosi Pebble car seat cosy toes can only be used in a MC Pebble car seat not in a Silver Cross Voyager as it will have been designed so the straps aren't obstructed).
A group 0+/1 seat like a Britax First Class which rf to 13kg then can ff to 18kg might suit you (be wary of the cheaper combination seats as they are usually group 0 /1 which rf to 10kg then ff to 18kg - they won't keep baby rfing for long).
Or you could get a Group 0/1 or group 0/1/2 rfing seat - the BeSafe iZi Kid X3 or X3 ISOfix (6m - 18kg rf only) or the Britax MaxWay or Hi-Way II (9kg/6m - 25kg rfing only) that can be used until the child is ready for a high back booster. There are also seats that can rf or ff to 18kg/25kg as well (the Britax Two Way Elite is rf/ff 9-25kg).
Hope that helps :-)