Oh, I forgot...I'm using Ernie Ball Power Slinky COBALT Flatwound strings on my full size 4 string basses?Forgot to add cobalt!
Which set? gauges?
I just got an Ibanez Mikro 5 string for my birthday. (...) The Mikro bass sounds kinda floppy with Dunlop stainless flatwound 45-125. Thinking bigger gauges would stiffen the B string a bit. Gotta confess, (...) Suggestions please!
Only Dunlop offers a short-scale, 5-string flatwound set: the DR Legend "short-scale" fiver set is actually 33.5" long ball to silk, and also has a .125" low B. The only operation offering custom-length flatwounds, Pyramid, only makes them up to .126".
For more options, you'd have to mod the bass (adding a string-through-body option) to accept long-scale strings (36–38" ball to taper, depending on the manufacturer), assuming there's enough room to do so. Also, you won't find flats larger than the .136" Thomastik-Infeld low B, unless you order from Octave4Plus.
What I'd do in your shoes is either tune up to C or D, as suggested above, or order a single
roundwound low B (135 to 145) and resign to having a mixed set. You could get a long-scale B and unravel it to fit the tuner (put a section of heat-shrink tubing or a drop of superglue where the unravelling stops, between tuning post and nut, just to ensure that...the unravelling stops), or order a custom-length one from the aforementioned Pyramid or Newtone.