Indio,
I note your scope is f/8, which is a very forgiving focal ratio - almost any eyepiece will work well with it - a 30-40mm Plossl will be fine.
The field of view of an eyepiece is limited by the diameter of the eyepiece field stop (a black ring inside the barrel) - or possibly the barrel itself if there is no field stop (as is the case with some eyepieces). For the widest field of view in a 1.25" eyepiece, this will be close to 30mm diameter. If you go shopping for low power eyepieces turn them around take a look at the telescope end to see how big the field stop is.
Some examples below, these are (left to right):
Four 1.25" barrels: Vixen LVW 5mm, 8mm, 13mm, 22mm
Then in the 2" barrels: LVW30mm, TMB Paragon 40mm, Vixen LV50mm. Note that the 40mm has a wider true field of view (no field stop !) than the 50mm.
Now I'm betting your scope has a 1.25" focusser. So as you can see in my example the LVW22mm has a field stop pretty much as big as it can be in a 1.25" barrel; this eyepiece is a 65 degree AFOV.
But... as Mental points out the maximum focal length in a 1.25" barrel depends on the design of the eyepiece - in particular the apparent (angular) field of view (AFOV). Referring to this table:
http://www.twcac.org/Tutorials/eyepiece_table.htm For a budget Plossl, the AFOV is ~ 35-40 degrees, the premium Meade and Televue Plossls offer 40-50 degrees.
You may find this calculator helpful too
http://www.twcac.org/Tutorials/magni...n%20Calculator