this is the one i use, works like a charm and dirt cheap! :) https://www.amazon.com/ThermoPro-TP49-Hygrometer-Thermometer-Temperature/dp/B07WCR5Y4B
The kitchen table is right next to the door that leads to our deck and that is the side the sun rises on.
I would worry about drafts from the door. As long as the door is rarely used in winter, it's fine. If there is a lot of traffic in and out of the door, I would move it away from it. Make sure it's not by a heating vent either! From what I've read, AVs do not like large temperature swings or hot/cold drafts.
So I'm thinking the light is poor, especially afternoon and on. I ordered this light on amazon and it should be coming today.
Is the room bright? They need less light than you think. I believe in the fall/winter/spring they can take full sunlight, but when the temperature reaches about 70-75 you will want to move them out of direct sunlight or change it to filtered light. Like put it behind a blind.
Oh and it's winter now, our heat is left on at 65.
From what I've read, optimal growing conditions are 75 degrees. They basically stop growing around 65, and under 60 is bad for them. You don't want to fertilize when the temperature is that low. I would recommend you buy an electric plant heating mat and setting it at 75F. I would also recommend you buy a small temperature / humidity meter.
Next you will want to make sure you're watering them from below, as in putting water in the tray and letting the pot soak it up. Put in some water, come back in a few minutes and see if it complete soaks it up, put in some more till it stops soaking it up. Feel the top of the soil so you get an idea of what that feels like.
Most people recommend watering from the bottom because water on the leaves will create dead brown spots on them, and it's much harder to over water from below. If you do get water on the leaves, dry them them off with a paper towel.
Make sure any water you use is at room temperature, this will minimize any thermal shock to the plant. If you have really hard water, I recommend buying and using reverse osmosis water.
I don't use an electric light, but I know some people here do. Maybe they can chime in on what is ideal lighting.
I just looked up the Milsbo greenhouse conversions and that is so cool! I def recommend monitoring the humidity I’ve noticed it does make a difference especially when the plant is younger.
I tend to monitor for dried out pitchers (weekly) in the crowns and pick them out so that there is more airflow in the crown and eliminate material that could potentially rot since I occasionally mist them in addition to using the tray watering method.
I have been using one of these: ThermoPro TP49 Digital Hygrometer... https://www.amazon.com/dp/B07WCR5Y4B?ref=ppx_pop_mob_ap_share
But if you’re building out a milsbo you probably could use one designed for a terrarium.
This is a great video of Cephs in their natural habitat, the guys commentary is fantastically colorful as well.