I t think I will wait until after the bike fit before I splash out my hard earned pension. I will mention it and see.
Like you I live off my pension and I'd encourage you to investigate sitting position, general set up etc. first. After your bike fit you should be much better placed to decide.
Personally I think shorts are the single most important piece of clothing. If necessary I would happily revert to low cost jerseys etc. but I'll never skimp on shorts.
I cannot recommend Assos highly enough for comfort, fit and overall value for money. Even at full retail, often £150+, their longevity, 3 years for me, works out at £50/year or £1/week.
About 15 years ago after much research and trying for fit I bought my first pair of Assos F1 Mille. These bib shorts are specifically designed for long distance comfort. I think they are discontinued but they do come up from time to time at:
https://www.assosfactoryoutlet.com
The full price is scary, £165, BUT sign up for the Outlet email and watch for deals. In the year before I retired I was able to buy 3 pairs at £90 each. A pair lasts me three years** and so I have ten years worth of shorts in my cupboard. I imagine Assos will have designed a replacement if you can't get these.
When I first purchased Assos I was very nervous at spending so much but it's a decision I have never regretted. Three tips from me, take the advice in the sizing guide (I didn't first time buying large when I needed medium), do buy bibs and take the time to go to a large retailer to try before you buy.
** these tend to wear out at the base of my spine which means by the end of year two it's a rather unpleasant sight. Usually the pad is still good and worn out pairs are comfortable underneath unpadded bib longs in winter - a big saving.