You didn’t say what platform you use, but if it’s Android, have a look at Locus Map. It’s very flexible with adding map sources, and comes with a decent variety in the standard set.
You add maps in Locus by editing a configuration file, providers.xml. I don’t know if it includes OCM by default, as I’ve been using a customized version of the file for years. But it’s easy to figure out the URL format and add it manually.
That said, I used to prefer OCM for everything, but have come to prefer the look of the offline maps (from Locus or OpenAndroMaps) which are very customizable through their use of themes. My current favourite is OpenAndroMaps V5 with matching Elevate V5 theme.
EDIT: there are some current difficulties with Android 11+, likely to be resolved soon.