Coolant on the foot well on drivers side is probably due to the heater matrix letting go.You may find that 1 of the small " 0 " ring seals from the aluminium pipes going through the drivers side bulk head into the matrix body has failed although to get that far you may be as wise replacing the matrix as access is very restricted.

Another classic sign of a failing matrix is a sticky film on the inside of the windscreen which is hot coolant vapour after it has dried.

Cost of a matrix is around £40 from a factors but the 2 small "0" ring seals from VX are crazy at some £3=50 each for a tiny rubber washer

,but they are essential to the fix.Only other costs would be coolant really.
The actual job is dealt with in 1 of 2 ways. Either spend several days taking the entire dashboard out and then refitting,or carefully cut sections of the drivers side footwell trim back allowing access to the matrix.Both methods are described in the maintenance section (although my limited IT skills don,t permit me to paste a link). I had a similar heater failure the early ..and cold part of this year and opted for the "cut,n,shut" method.It is actually very straightforward and if done with care the finished result is practically invisible.
Only slight issue I found was that the aftermarket matrix did not have the sealing foam on each end to allow a tight fit inside the craddle and required some modifications with bits of draught excluder to avoid a passage of cold air constantly blowing through the gap and onto your feet.Also when heater is now ussed on Hot the plastic casing does give off a slightly strange smell which I have now got around by hanging an air fresherner in the footwell...small price to now pay for having heat again as when mine went footwell and my feet got a very wet shower...carpet also took an age to dry out and stop smelling .
Best of luck..its not to bad a job