Have you checked the morale report? Most likely you are getting a massive negative morale from not resting (there is a bug where even if you turn off this feature in mod settings, it still accumulates negative morale). It's very simple to address, just go to any town and wait there overnight. In the morning you should get a message that your morale improved form resting. If the penalty was large the bonus will be large too.

Otherwise, no I haven't had a problem with it. Decent food, keeping your party size low and an occasional scuffle is all I need. Only when I neglect rest do I have problems. Also note that if your rank increases your party size limit gets huge and you practically never get the "party size unmanageable" penalty. I only see it now when I max out my party for a siege.

If you have happy widows, huntress, camp defender, etc in your party, there's a dialog option with them now about morale.

You can ask the Emperor to declare war on another kingdom. Party moral also highly depends on party size: if you run around with a full party it is very difficult to manage, if you only have a small party then it is easy. You can also pay your troops additional wages in the camp menu. I usually only run around with a large host if I want to raid villages, or if I want to besiege a castle/town. Btw, if you have a companion you can order him to lead his own party, (but choose a companion with a high leadership skill) then, when you have created the party and given men to him you can order him to 'attach to your party' this means, that his party will be in your party (like lords sitting around in towns), this is very usefull if you want to have a huge army, without keeping that much attention on moral (but unit upkeep of troops in compaion parties is higher I think)

If you need someone to fight during peacetime, go to Jerusalem and fight the Judaean Rebel parties in that area. They spawn a lot of big parties and the jewish rebels are great to farm since they're very high level so they give great xp and the prisoners sell for 450 each. They're also very aggressive so they'll chase you even if your party is much bigger. Just don't underestimate them. They look like looters but they hit pretty hard.