Dungeon Master Guide, page 165
Dragon Scale Mail
Armor (scale mail), very rare (requires attunement)
While wearing this armor, you gain a +1 bonus to AC, you have advantage on saving throws against the
Frightful Presence and breath weapons of dragons,
and you have resistance to one damage type that is
determined by the kind of dragon that provided the
scales (see the table).
Additionally, you can focus your senses as an action
to magically discern the distance and direction to the
closest dragon within 30 miles of you that is of the same
type as the armor. This special action can't be used
gain until the next dawn.
The armor has also base features of a scale armor, which means:
- it will grant AC of 14 + 1(magic) + Dex modifier (max 2)
- disadvantage of stealth
If it is not enough, you could make this item legendary, by increasing the armor bonus by 1. Then it would grant 16 + dex mod (max 2).
If your character relies on stealth and high dexterity (16+) you could get feat Medium Armored Master to negate armor's disadvantage and increase max dex cap to 3.
Anyway it appears that you have missed the most important Rule 0.
The D&D rules help you and the other players have
a good time, but the rules aren't in charge. You're the
DM, and you are in charge of the game. That said, your
goal isn't to slaughter the adventurers but to create a
campaign world that revolves around their actions and
decisions, and to keep your players coming back for
more! If you're lucky, the events of your campaign will
echo in the memories of your players long after the final
game session is concluded.
Dungeon Master's Guide, page 4
Your players may dislike it but, as Game Master you can create anything that you would like to. Although you shouldn't ruin the fun for everybody, as it would be simply immature.
Druids have problems with metal equipment? Why won't you make a full plate armor made from draconic bones, skin of Tarrasque, scales of Bahamut/Tiamat or pure diamonds. Anything is possible, use your imagination! That is what role playing is about.
You should try to find out the consequences yourself, however if you find it difficult, there are possible consequences, which I often use:
- The weight is increased or decreased, maybe even multiple times in comparision to the original.
- Change of the value.
- Unique materials are needed to maintain the armor's performance. Blood, grease, saliva, extract from unique species.
- (for magic armor)The items work only, when all pieces of the set are gathered.
The more positive aspects may be based on already existing ones or the source of the armor.
- Granite breastplate weights 3 times than normally (60 pounds), costs 300 gp and has a disadvantage on stealth tests.
- Shell full plate armor costs 2000 gp, and weights 50 pounds and must be regularly treated with Plesiosaurus' mucus.
- Diamond full plate armor is priceless, gives immunity to critical hits and resistance to physical, non-magic damage.
- Hide made from Sahuagins gives advantage for underwater stealth tests.