Shower is too cold, despite cartridge setting
My solution has nothing to do with plumbing, but since you mention the problem is in your basement and only in the winter, I'll throw this out there and it may help others...

I live in an apartment on the top floor of a renovated historic building.  I like hot showers, and never was happy with the temperature of the water in the shower.  It was passable in the summer, but taking a shower became miserable when cold winter weather set in.

For a long time I assumed the problem was that the water cooled down while traveling through pipes up to the top floor from a water heater that is presumably in the basement, and that lower ambient temperature in the winter made that worse.  I doubted the landlord would change the water heater settings just for me, so I was all set to buy one of these and this and this to fix it for myself.

But then I realized that the cold air in the bathroom was at least partly responsible for my discomfort, since I was shivering as soon as I turned the shower off.  So I made two simple changes.  Before every shower, I closed the bathroom door, and blocked off the vent fan with a plastic bag, which stays stuck to the vent cover from the suction of the operating fan.  (In this bathroom, the fan and light are controlled by the same switch.  If the light is on, the fan is on.)

It made a huge difference.  Since I don't turn up the heat that much in the apartment, showering with the door open and the fan on was pulling a basically unlimited supply of cold, dry air into the bathroom, and it was the evaporative effect on my skin making me feel extra chilled.  But it's not just that the air temperature felt warmer.  The shower water that had felt barely lukewarm before now subjectively felt hot.

I later added a space heater set to 65°F and that made the showers hot enough to turn my skin pink (the way I like showers).  Someday I might swap that out for one of those electric towel-warmer-radiant-space-heaters.

So, to summarize, if you feel the water temperature in your shower is too low, you may be able to adjust your subjective experience of the water temperature by raising the air temperature and/or humidity in the bathroom.