Well you can splash monk and still have mass heal ( think lv17 cleric gets you that )
But building to AC is a huge grind to get the very specific items you need to have an ac that will do anything at all .( AC does nothing until the creatures you are fighting need more than 2 to hit you , often without having a lot of items you just wont cut it )
this build http://forums.ddo.com/showthread.php?t=292100 has a list of itemsyoud likely need tohave a workable AC .
The best reason to splash monk 2 though is for evasion , but even then you need to work towards a decent reflex save .
I would recommend on a first life cleric you are better sticking cleric 20 as it gives you leeway on your healing ability while you learn the tricks of the trade and to look for the items you ll need in future lives to make thinking about an AC build possible ( you are always best with an AC build ( and most other builds to be thinking about it from creation )
Randomlysplitting of from your original class can be hazardous if you dont concider all that yyou lose for what you gain