Graham s I to ride a tdf and have swapped to a charge spoon best move I made could not get comfortable on standard saddle and suffered on long rides as for the stock tyres don't think its anything to do with weight pal mine only did 800 miles and had to be changed was sick of punctures and I'm a mere 13 st .
One of my mates might have a compact going spare which I can try out, but failing that the cassette option seems to be the best. I don’t know what it is like round your way but there is a place near me called South Harting which was a killer hill, touches 30% in places. Tried it twice with current gearing and am nowhere near being able to do it in one go. At the moment I am scared of it and it is annoying route planning to avoid it. There are a couple of similar climbs near me plus loads I can do now, but could do quicker with more gears.
The Charge Spoon has a good rep and you’ll get some change from £25.
My tyres started puncturing on exactly 1,000 kilometres, it was eerie, like an apple product failing as the warrantee ran out. My wife thinks I jinxed them by saying “1,000 kilometres without a puncture, that good going aye?”. (I switched to thinking kilometres to make it easier to feel inadequate when watching the Tour De France). Currently have some £8 Vitori Zaffiro’s on my bike but will upgrade them when I can.
And lighter wheels, combined weight of 3.5kg for the wheels on the TDF, saw some deals on Merlin Cycles website where I could get wheels under 2kg combined for £80ish. Should make a big difference.
I have skinny friends to keep up with!