Re Ambrosia, I have found quite a lot of it in the many dungeons, caves, forts, etc., usually one bottle in almost every one. Usually you have to search very carefully to find it, often in some place that is out of sight such as a ledge or pit, but I have more than I can use. I rarely use "found" or "bought" healing potions, I use alchemy to make my own which don't raise arcanic fever. I rely quite heavily on using food to restore health, especially the type you make at a hearth such as soups, roasts, etc., or the ones you can buy from a bakery such as nut rolls, etc.
If you are level 19, I would suggest you haven't explored as much as you might think. In my first play-through, I did all the side quests and explored everywhere I could, and I was about level 75 before I started the main quests (i.e. going with Jasper to the Sun Temple, etc.).
I don't know about shields, I just equip one for the armor bonus but I don't try to block. I mostly use bows & 2H, but I haven't used blocking in any of the Elder scrolls games, as shields don't impress me much.
You didn't mention what difficulty you are playing -- adept (normal) or one of the higher ones. I think the game is easier if you rely more on doing as much damage as possible at a distance (from stealth, with bows and spells). If you are having mostly close-up battles with 1H, for me that would be very difficult.
Re heavy armor, the Ratcatcher set is rather low-level. I checked my chest for "set" heavy armor for my old character, and found my heavy body armors as follows: Ratcatcher 34, Selna's 48, Fallen 58, Skaragg 78 (levels as shown in the chest, not as equipped).