I'm not sure we can help as you must make the decision.
Firstly, Febi Bilstein is OE, I think and will be the best quality product. I don't see how the mountings will influence ride height. They only really provide a compliant location for the damper rods.
The springs are the major factor in ride quality. The dampers control how they work so standard, softer springs will iron out imperfections better but worn dampers will make any set up poor.
I'm not happy telling people what to do but I can offer guidance.
KYB never produced any components for 156 Sportpack/Veloce suspension. I don't know what the suspension spec of 147s was. All I know is that there was not an option for standard or sports. No one has measured standard ride height for a 147 and posted measurements, so I don't know. There does seem to be a bit of variation but this is not surprising as the cars are a bit older now. I have some conflicting but possibly spurious information about that so I just cannot say.
If 147 suspension was based on 156 standard suspension, nor Sportpack, then KYB never actually made any dampers fit for a 147. Sports suspension cars should have firmer dampers but no one can say for sure how it will perform in respect of a particular owner's preference.
Ideally, I'd rebuild the Bilsteins. I don't really see much advantage in using Koni dampers (other than flexiblity to use standard springs).
I don't think non Koni/Bilstein dampers would be a great idea with H&R springs but it is more important at the front because the front unsprung mass is greater.
If changing springs, given the current set up which is not firm like Apex, Leda etc in your opinion (from what I know, I'd tend to agree), I think Koni Str.T front struts with TRW rear ones would be the way to go.
Doesn't really help, does it?