Bit late to the party JB but as the owner of a 66 plate Toyota Yaris I thought I would give you my two pennies
Despite the fact that Ridders originally christened it the granny car its surprisingly good, well equipped , and a very relaxing drive.
Don't believe the book figures for economy .. mine does just under 60mpg driven relatively conservatively (I'm an ex Ford ST hooligan !) but that is still not bad for petrol , its very comfortable , easy to park ( no jokes please !) and not that small , you would easily be able to get little one in and out of the back if you needed to , Isofix as standard so you are fine there.
Ridders is now completely converted although unwilling to give up his man truck to get one of his own
If you are in the vicinity of Sussex any time soon you are welcome to a test drive