Searching a directory for copies and renaming them

Im trying to create a script which will find two files in the same directory with the same name but different file types and change one of them, for example filea.txt and filea.jpeg It will then change one type to another name while keeping the file. Example filea.jpeg now becomes filea1.jpeg I was thinking some sort of if loop to check the files agaisnt eachother but when i attempt to do it i end up nesting many loops. I also have was trying to implement and if loop for the name change example but honestly have no clue where to start any help would be much appreciated