The 15mm and longer focal length GSO plossls are great value-for-money EPs. I suggest you use them with a barlow for higher powers. A barlow will preserve (extend a little in fact) the eye relief of the eyepieces.
A GSO barlow would be okay if you want to keep cost down. But atm AEC have Televue 1.8x barlows (which is an older model) for $130, which is probably your best option. I just ordered one over the phone and they tell me they have a "few" more. See
AEC website.
PS. I guess you mean EQ mounted Newtonian - Dobsonian is a Newtonian on a specific type of alt-az mount.