I'm terrible at getting the right texture for soups and stews. Adding boiling water to adjust the texture right before serving is my usual response. Would this work as a long-term solution, or does it affect other aspects of the taste?
This will also water down the flavour of the soup. Depending on the type of soup you are making you may have some cooking liquid left over which would be far preferable to plain water.
In fact it's not a bad idea to start with a little more cooking liquid than necessary. Use a fine-mesh sieve to separate the soup ingredients from the cooking liquid. You can then re-introduce the cooking-liquid a bit at a time until you arrive at the right texture. That gives you a margin of error.
Adding milk, cream or sour cream are also possibilities, again, depending on the soup.