Kvadrat Field for a Tecno D70  

Was the sofa with Field fabric reupholstered or was the sofa produced with that fabric? Personally, I would not put a 100% polyester fabric on a sofa that was designed in 1954. (I also just don't like the feel of poly fabrics but that's a personal thing.)
http://kvadrat.dk/collection/detail/uid/5298-0142/all-colours/show
I think a wool would be a way more authentic choice but if these sofas were produced more recently with synthetic fabric, then ok. The Lana Diagonale is wool, for what it's worth.
I don't know Italian fabric mills at all so I can't suggest an Italian wool, but Kvadrat (a Danish company) makes a few that I'd seriously consider if I were reupholstering this piece.
Photo #1 is Hallingdal 126 (166 is the same but with black and white threads). This has a very wooly texture, not what I think of when I picture an Italian suit---and it's rather scratchy if you are bothered by that characteristic of wool. But it wears well and looks great.
http://maharam.com/products/hallingdal-by-kvadrat/colors/126
Photo #2 is Steelcut Trio, also wool but with a very smooth texture, closer in looks to the polyester Field. The subtle striations you see in the photo are for real and are an intentional characteristic of the fabric--some people prefer a cleaner (?) weave.
Both of these have a smaller scale pattern than the Field, I think, but definitely big enough to see when you're sitting on the sofa. I think "playful" is a very subjective term so I can't say if it applies to them or not.
Where are you located? If in the US, you can get swatches from Maharam but if you want to order from them you either need a resale tax number or your upholsterer has to order. (Unless you find the right color and yardage from a third party online or locally._

Hi Spanky,
Sorry for my late reaction, things are a bit hectic for the moment.
Thanks for making some time & weighing in with your experience and feeling.
It's always much appreciated.
And you've touched all the right buttons 🙂 I agree about the polyester.
The dealer of depicted sofa stated it was reupholstered
using a kvadrat fabric. As I went to the Tecno sheet, I saw 'Field' being offered
as one of their optional fabrics. I assume they used this fabric from
when it was introduced by Kvadrat.
My experience is that Tecno shifted from domestic clients to much more
office orientated products, over the years. In that sense it wouldn't surprise
me they offered a polyester based fabric like Field because it's more suited
to a slick office environment?
I assume I would be bothered by the feel of poly, but I do like the bold
structure. Then again, I agree on what you say about Hallingdal; I am always a bit
bothered by the scratchiness...
So we move on to your other proposition, the steel cut trio. I like the striations (lovely word)
a lot, it gives some subtile movement from afar.
Browsing through the Kvadrat catalogue I've also encountered 'Masai' by Raf Simons.
It's wool based, with a little nylon and has the same diagonal look as the original tecno fabric,
but with a much more 'busy' appearance.
I'll order some samples of the two and judge on feel and eye.
Thanks a lot!
Keep you posted.
https://kvadrat.dk/collection/detail/uid/1248-0162/all-colours/show

Ah, sorry--I missed what you said in your first post about "Field" being one of the options offered by Tecno.
I like the Masai very much! I have never seen it in person because Maharam doesn't carry it and as far as I know they're the only distributors of Kvadrat fabrics in the US. It's listed as 90% wool and 10% nylon, nylon being typically added for durability.
I also like the little bits of blue in there. They will give it close-range interest. Good choice!