As
@vickster mentioned.........I am the world expert on sore a***s
There are so many variables that may affect you.
When I was young I could ride 50/70 a day with no padded shorts. Having gone back to cycling in my mid 60s I quickly found my sit bones were no longer elastic. I bought a pair of Funkier short (£30ish) but if managed a 30 miler I literally could not get back on the bike for a week.......it was sooo painful.
Went for a £100 bike fit and bought a Sella Italia saddle.............made no difference**.
Spoke to the manager at a LBS who got me on a turbo and said.......that set up is all wrong and that saddle is wrong for you. He re-set everything and sold me a Fizik and a pair of Endura shorts. Next day I went out and did a 68 miler.............got back on the day after and did (I think) another 15 miler. What is more he didn't charge me for the fit.
**got all my money back for the 1st fit and saddle.
So my point is....................
I don't know the answer
I am sure it is not just a pair of shorts/or a saddle/or a bike fit.
Depending on which part of North Wales you are............it may be worth a trip to Warrington and get this guy to check you out (not saying he does it for free every time though)