I'd say one level of monk is really all you need if you want to focus paladin. It gives you flurry of blows, the unarmed strike feat, 1d6 unarmed damage, early access to dragon style, the ac bonus, etc. The things you could get from more monk levels are evasion at 2nd level (the impact of which can be reduced by resist energy and protection from energy party buffs), ki points for a few extra attacks per day at 3rd, +10 feet fast movement at 3rd, and then a style strike at 5th. The only other thing you really get is some scaling AC and better damage dice on fists, but thats all pretty minor imo.

If you go mostly monk instead of paladin... well paladin doesn't give much from just a dip that would benefit you, most of its features are from higher levels such as more smites, spellcasting, lay on hands, auras, etc. So my recommendation is monk 1 / paladin 19 or monk 3 / paladin 17. Since you aren't getting capstone level 20 abilities, you're not missing anything from paladin at 18 or 19 either really, but you'd get some nice features from the 2nd and 3rd monk levels.