It looks like your plant would benefit from more light (these are not really great shade plants). As much sun as you can provide indoors during the winter.
The pot looks quite wide for the size of the plant. Which could be just fine, but my preference is to match the size of the pot to the plant, especially the roots, so it's not a whole lot larger. You probably would benefit from more rock in the mix too (like half pumice or perlite maybe), which makes the watering easier.
When you consider how often to water, try to remember that the natural cycle of growth includes a thirsty time when the plant is leafy and stems are growing, and a relatively dry time when the plant goes leafless or slows way down. Too little water during active growth can bring the plant to a halt, and too much water during the dormant phase can make it rot. Try watering your plant differently depending on the season (max in summer, min in winter) and its state of growth. The difference might be 2-4 fold in frequency, depending on the actual conditions where the plant is growing. If you can provide very bright light and good airflow, that will help with the watering.
Remove any soft spots with careful surgery if you can, and let the plant heal afterwards. If you think the caudex is lost but the main stem is salvageable, try cutting it (through healthy tissue well above the rot) and then you can try to root the cutting.
