You're best off getting down to Sabre Sales in Portsmouth, they've got loads of 1950s dated wool shirts, trousers etc for hardly anything and will look much better than those.
Another good shirt option is a collarless cotton khaki 'grandad' shirt off ebay.
A lot of the guys with wool alergies use though and if you remove the breast pocket (if they have one) they look spot on til you're close up.
You can get original denims for not much more if you shop around.
I got my denim trousers (repro) for a tenner off this forum and my original 50s denim jacket (53 dated but 40s cut) for £9!
If you're willing to take the risk of it being late/not arriving then replicators can do you a full repro set of WWII denims for very little.
If you do go for the brit lightweights and shirt option, buy them far bigger than you need if you want them to look like denims.
"I think we are in rats' alley - Where the dead men lost their bones."
Also if you're rather slender, you might be able to get a Dutch BD set (blouse and trews) for under £30.
I got mine on ebay for about £21 from a seller called sfrankish.
I also use the shirt you linked to wear under my BD.
