I would like to add 2 more position players who are eligible, one will be a slugger and one will be a defensive specialist.  I already have a good SS who will play against righties but can't hit against a lefty.  A lesser defensive SS will play against lefties but he can hit pretty well for a SS.  I have an all-star caliber CF who will play all game and a very good 2B.  Here are my two defensive options:

1) Estrada - 2B/CF - great defender and great pinch runner.  
B/T: S/R
RNG: 89
GLV: 86
ARM: 60
ACC: 54
SPD: 96
BR: 70
CNT: 18
PWR: 34
VL: 87
VR: 17
EYE: 71

2) Mendoza - SS/3B/CF - better overall defender and can play more positions.  Not as good at BR.
B/T: R/R
RNG: 94
GLV: 81
ARM: 92
ACC: 87
SPD: 46
BR: 59
CNT: 60
PWR: 19
VL: 61
VR: 16
EYE: 50 

Here are my two slugging options

1)1B - better contact, power, and eye.  Worse splits.
B/T: S/L
RNG: 38
GLV: 34
ARM: 44
ACC: 34
SPD: 50
BR: 39
CNT: 64
PWR: 92
VL: 38
VR: 44
EYE: 92

2) 1B- Better splits and worse contact, power, and eye
B/T: S/L
RNG: 35
GLV: 39
ARM: 31
ACC: 38
SPD: 46
BR: 23
CNT: 60
PWR: 78
VL: 72
VR: 52
EYE: 73

I'm leaning toward adding the 1st option in the power hitters but I'm torn on which player to add for a defender.  The SS might see more action in the field but will have little to no impact on the lineup.  The CF may play some in the field but will see some action as a pinch runner and will be my best option on the base paths.  

If you don't need a 3B/SS back-up, the other player who can run is the obvious choice.