Just be aware that if you buy the replacement car before selling the 147, you'll need to SORN the 147 or risk getting fined for having an uninsured car (it does happen - my daughter got caught after trading a car in, that wasn't then taken out of her name).
I had a 159 2.4jtdm and absolutely loved the car. The engine is an absolute gem, but does encourage enthusiastic driving - with the result that I only ever saw 35-36mpg out of it. Handling-wise; you will notice the difference from having that very heavy diesel lump way up front; it holds the road extremely well, but won't have the light on it's feet, darty feel of the 147.
Your heart will certainly say 159 2.4, but maybe your head is telling you a 159 1.9 diesel is more sensible for a 100 mile a day commute? Surely a 1.9 would tick the boxes a Passat ticks and remove the (unnecessary?) expense of running two cars?