I would defnitely go with a small tetra. The larger ones will eat the adult shrimp as well as the babies, so none of the skirt type tetras would really work. I would not go larger than a cardinal/rummynose tetra.
Its true that any fish will take advantage of free live food (i.e. baby shrimp). With areas of dense planting, a fair amount will make it to adult hood. The adult shrimp are too large to be eating.
Normally I recommend an invertebrate only tank as well, but 125g of invertebrate only is a bit excessive.
I would do ember tetras, or even something like a microrasbora (you could fit hundreds in, literally as they are smaller than the shrimp by far). Then a cory or a dwarf cory or otocinclus. Another option would be ancistrus plecos. You could even get away with pencilfish or hatchets for the top level. This tank, depending on what species of tetra/rasbora you choose, may not even need a heater.