If you want to move more than ONE or TWO positions...
...the best choice is to hit
ESC, move around, and get back to insert mode again.
There's no point on create mappings like
<C-h> to move left and then start hitting it too many times... as a vim user you're not supposed to hit the same key multiple times to achieve a smart movement.
ESC key isn't close to your fingers, it would be a good option to create a mapping for it.)
If you want to move ONE or TWO posistions on insert mode...
...a good choice would be to define some movements using your
<Leader> key since it's feels close and confortable to my fingers)
noremap! <Leader>h <left> "move cursor left
noremap! <Leader>j <down> "move cursor down
noremap! <Leader>k <up> "move cursor up
noremap! <Leader>l <right> "move cursor right
noremap! <Leader>w <esc>wi "move one word forward
noremap! <Leader>e <esc>ei "move forward to the end of word
noremap! <Leader>b <esc>bi "move one word backward