I have big legs. I've been trying to come up with clothing for cold weather, but the legs and feet remain a problem.

I found some long johns that have 8% spandex, and I did a ride with them yesterday. They worked. They aren't the last word for warmth, but they move easily.
https://www.duluthtrading.com/s/DTC/...html?color=BAH


But I am still looking for ways to keep my legs warm, or at least warm enough to avoid hypothermia. So if you have any suggestions..

depending on temps, wind & precip I use a variety of things to get me thru to colder months
I start with Novara brand cycling pants
add generic running tights, under
remove tights under & add Showers Pass brand rain pants over the cycling pants (even if it's not raining)
ditch all that & wear just lined tech pants (Eddie Bauer brand)
some days I've worn EMS brand fleece pants, that I normally use as pajamas, w/ Showers Pass brand rain pants over

Maybe long wool socks may help.

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Long thermal pants with a reinforced back (e.g. Cordura) is what I dream of, but alas.

Good places to look for base-layer are Craft, Terramar and Karrimor. I get cold easily (low core temp), but I'm fine with medium-weight base layer, as long as I have rain pants (a "shell") over them. I'm still using my old REI Thaw pants over my Terramar Merino Wool ( 30% Merino Wool), but should get a pair of Mountain Hardwear Returnia for this winter, because the water repellency of the Gore-tex is failing. Aerotech Designs offers a "tall" option, that may be a good fit. They will actually custom-make an item for you, at no added expense! https://aerotechdesigns.com/mens-thermal-tights/

The rain pants are key. If it's cold enough, your legs won't be sweating, so the rain pants being waterproof is irrelevant.

Back when I was still bike commuting, on the coldest days (around 10 degrees F and under), I added gaiters to cover my shins and ankles. I also used flat pedals and toe clips without straps and wore insulated work boots.

I have some "winter weight" cycling pants that work well enough in cold weather. When I am not cycling and it is cold outside I will wear TSLA thremal compression pants that sell for $10. Under my jeans they help a great deal. I avoid wind or rain pants as they do not breath and so I am wet from the inside out with a lot of physical exertion.

As others have stated, it depends a great deal on the weather conditions. Of course, I can see that many of us will have our specific preferences. I tend to prefer multiple thin layers in as much as possible, starting with silk, which makes it easy to use a second layer on top, which in my case is a Marino wool blend.
In milder winter weather (up to ~20F), just the silk layer is adequate. I do use two layers of socks, a calf high compression socks and thin pair of woolen socks (my feet tend to get cold). When the temp dips down to about 5F, I have a second layer of fitting underpants made from Marino wool with some synthetic material blend - wish I remembered the name (I always cut off all the tags so they do not scratch, which means I can’t tell you the name of the brand but I’m sure there are many - mine were rated at medium weight). Second layer of socks are made from thicker wool. Between about 5 through -10F, I use a third layer of underpants which is a thick fleece. Even when not windy, I wear a wind-proof layer over the pants, which makes it the 4th layer. My feet have three layers: compression socks, skiing/sports socks that are calf high, and thick woolen socks. If it is a windy day, I may also use wind-proof shoe covers.
I stop bicycling when it hits -10F!

Stay safe and warm.

If I'm wearing pants and I want a layer under them, cycling tights are enough for me. Sometimes they make me too hot.

More than one pair of long johns? I'm tall and skinny. A poor setup for delivering warm blood to toes. In my Boston and Ann Arbor days, I was known to use more than one layer of LJs.

Also (and this is big!) be sure you have full wind block on the fronts of your legs, especially thighs down over the knees. I used newspaper back in the pre-miracle fabric days over my thermals and under my riding tights or regular pants. Now I use wind front tights. I've also started using gaiters I made of windblock, semi-stretchy fabric and velcro over my ankles. I made them to shed Portland's rain on long rides but quickly found they were very nice in the dry cold. And I still sometimes cover my thigh fronts with plastic bag or newspaper to stretch the temperature range of what I have on hand.

For my long (and very long for my waist size) leg, I also make it a point to wear high socks that overlap fully with the thermals.

For me, the biggest thing is that I have to keep the warm blood I send down there warm. All of that blood is very close the surface around my knees. (I want to get them re-plumbed al-la bike hydraulics that run through the headset and bottom bracket but I am holding off until I can get those replacement ti knees with the proper hydraulic blood lines pre-installed. Perhaps not this lifetime but maybe I can spread the word and they will be around for the next.)