Clear water needed?

[Oblio]

So I could get away with the poly fibre and sponge?

Yes. There is differing options on sponges vs ceramics for bio media. I use both, along wit a pre filter sponge on the intake.

Pic below is lengthwise of my tank, tip of driftwood is about 170 cm away from near end of tank. Bubbles are from HOB outflow and currently battling Cyano outbreak so the is a bit of haze on glass that was cleaned Saturday.

 

[Oblio]

Better pic with lights up

 

[Essjay]

Fluval U filters have sponge, polycarbon pads and ceramic medium in the centre box. All you need to do is swap the polycarbon pad for filter wool.

I would be careful of using filling intended for pillows etc as most of the stuff for sale in the UK has fire retardant chemicals. I prefer to err on the safe, if more expensive, side of buying a length of filter wool from a roll and using the original medium as a template to cut it up.
https://www.amazon.co.uk/s?k=filter...=filter+wool,pets,67&ref=nb_sb_ss_c_2_11&tag=