[Haskell-beginners] Maybe problems converting back to number

[Galaxy Being]

I've got this example from the Internet

import Data.List
import Data.Maybe

firstFactorOf x
    | m == Nothing = x
    | otherwise = fromJust m
    where m =(find p [2..x-1])
          p y = mod x y == 0

and this as a crude return the nth element of a list

import Data.List
import Data.Maybe

-- myIndex :: [a] -> Int -> Maybe a
myIndex [] _ = Nothing
myIndex (x:xs) 0 = Just x
myIndex (x:xs) n = myIndex xs (n-1)

I would like the Just x in the second block to actually be fromJust x as in
the first block, i.e., I want a number returned, not a Just typed object.
I've tried changing Just x to fromJust x but get the error when I try to
use it

> myIndex [1,2,3,4,5] 3

     * Non type-variable argument
:         in the constraint: Num (Maybe (Maybe a))
:       (Use FlexibleContexts to permit this)
:     * When checking the inferred type
:         it :: forall a. Num (Maybe (Maybe a)) => Maybe a

What am I missing here? Also, my type declaration seems to be wrong too,
but I don't see why.

LB
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