You might have a bit of trouble finding a significant upgrade. When I was first looking for a ML that could shoot well with open sights, most opinions were that the Triumph's stock comb height was not very well suited for shooting without a scope. Meaning, if you wanted to mount a peep or ghost ring further back on the barrel (closer to the breach) it became hard to get your head down low enough to get a decent sight picture. Of course, you (meaning your head!) may fit better.

Hope you find something that works.