Myprotein has a French site too, it will likely redirect you there automatically when you register.
Granular lecithin isn't sold by them but usually you can find it in food stores and pharmacies, it might not be so easy to find sunflower lecithin which is preferable because the extraction process is just pressing (while with soy needs solvents not necessarily friendly) and there are no phytoestrogens (unlike with soy).
What seems to be an excellent source for it:
https://www.teetraeu...5&referid=20162
By the way consider supplementing it too (1,2-5g/day), it is off topic here but do your own research and find out why.
Don't expect miracles from topical creams or gels, what you can easily and cheaply make at home can compete (and often win) with the most expensive and branded products on the market, certainly without all the chemicals they have to use in order to guarantee long shelf life, appealing look and smell, etc...
That said as a rule of thumb what you can expect is moisturizing, antioxidant and exfoliation.
Some specific issue can be addressed too but in general those are what is welcome by everybody.
As moisturizers HA gels and lecithin work very well, oils and butters do work but tend to be comedogenic, if one isn't concerned about that issue there is an endless list but in the end if you look at the composition usually there isn't that much difference, I might suggest emu oil, red palm oil, coconut oil and castor oil (not by itself but blended in one of the others).
As antioxidants ALA is one of the best I can think of but there are a lot of antioxidants which can be used topically, basically all, from grape seeds extract to ascorbic acid, each comes wit its own advantages and downsides but in the end I doubt it would be necessary to go mad about finding a magic one, what they do is basically the same, choose one you like and be happy.
ALA doesn't solves in water but a really tiny amount does a lot, doesn't stain or irritate (it stings a bit if too concentrated and is unpleasant if inhaled but liposomal should minimize those and anyway it's bearable).
Exfoliation can be achieved with urea but my somehow preferred is glycolic acid.
Glycolic acid is usually referred at as a peeler, well, after many years I have never been able to get a real peeling out of it regardless of concentrations, it is more an exfoliation (you don't see layer of skin coming off, actually you see nothing of the kind at all), best concentrations are below 10% used everyday in cycles.
Urea is handy on calluses or hard skin as a softener, on face I prefer better glycolic acid, but that's just me.
Pantothenic Acid might help with acne.
Vitamin C tends to irritate causing inflammation and even burns, I don't like it, I'll recommend low concentration and/or buffering it with baking soda.
I doubt it would be very effective or even possible to boost collagen production with topical lotions, it pertains to a much deeper biological level with its own bottlenecks unlikely to be addressed topically.
EGCG is mainly an antioxidant but topical tea might exert a subcutaneous fat reduction and you DON'T want that, believe me.
Melatonin is an antioxidant but its low molecular weight allows for crossing the skin barrier, before sleeping can be interesting, it is water soluble (you can add it to HA gels).
Ferulic acid is another antioxidant which might help to reduce dimers formation due to UV exposure too.
Pterostilbene might be interesting for its chemoprotective effects
But something eludes me: "to use underneath sunscreen", if one uses sunscreen what for the use of protection at cellular level?
Sunscreen doesn't allow for radiations to reach the cells in the first place, end of the story.
I don't like sunscreens, never used one, are loaded with compounds I rather prefer sun radiations to, but that's just me, of course.
Nicotinamide riboside...don't know about this one, would it be much different than nicotinamide and ribose?
Much more expensive for sure.
Everyday use, mmmm.....maybe every other day (alternating mitochondrial fission and fusion)...but wouldn't be better as a supplement instead?