Travelling in early autumn without taking jeans

I’ve booked a holiday to Europe in September this year. I’m flying into Paris on the 3rd of September and will spend around a week and half in Paris, Lyon and Provence before flying to southern Spain.
Google tells me it’ll be low to mid 20’s Celsius in France at that time but once I get to Spain it’s going to be in the 30s.
I need to keep the weight down in my luggage as much as possible so I can still do my fabric shopping in Paris as planned and meet the weight restrictions for my internal flights.
I’m planning to take a couple of pairs of wide leg linen trousers for the warmer parts of my trip but I feel they’ll be just a little too cold for France at that time in the evenings.
I’ll also be packing some linen or cotton dresses, linen midi skirts, a merino jumper or two and at least one pair of running tights to wear on the plane (long haul flight).
Looking for suggestions on how to dress linen up to be a little warmer? Should I be looking at a pair of tapered leg trousers for more flexibility in my outfits?
Note I sew most of my own clothes (which is why I’m thinking about this now) so I can tailor specific style ideas to warmer or cooler fabric options as needed.
Also I was planning to pack only white sneakers and comfy sandals but I’m wondering whether it’s worth packing a pair of loafers or whether that just defeats the purpose of not taking jeans 😆