Morning Tarquin
Welcome to the Forum (almost)
Most cars now have an extra storage compartment under the boot floor these days where the spare used to live.
Not sure about your comment about a raised boot floor unless the car had a sliding floor for easy loading
Not sure what dogs you have but I have 5 HPR pointers and while I have an X5 my wife has a Subaru Outback and our daughter has a BMW 320d touring. All 5 are fine in the X5 4 are comfortable in the Subaru or the 3 series (The boot is around the same size height in both)
Maybe look at a 5 series Touring, good hunting
Dave