What is the lowest-level spell combo to give disadvantage to an enemy’s specific save, without running into follow-up concentration issues?

What I’m trying to do is debuff an enemy’s stat so that I can hit them with a “save or suck” spell like dominate monster, and be more likely to succeed.

The problem is, I’m running into concentration issues because most spells that debuff a single stat like Bestow Curse use concentration, and thus I cant use them in conjunction: The moment I cast Dominate Monster, Bestow Curse is removed.

Hex also will not work because it only impacts ability checks, and not saves.

To clarify, I am a Warlock who wants to cast powerful disabling spells only when they have a high chance of success (so typically Wisdom has to be the weakened modifier). However, I am open to answers outside of that class, as well as any spell combos that specifically function as

  1. Weakening the the ability save for the second spell without utilizing concentration, and

  2. The second spell being a powerful, one-save spell of concentration.

What spells would be the best for this kind of combo, given that only I can cast the spells?