Hi Cris and welcome to IIS!!
Congratulations on your new scope, and well done on getting a target. Mars is always a tricky one. It is veeeeery small and this apparition has not been a great one although it was quite high in the sky at it's best. Now though it is getting smaller and lower in the sky which makes it more subject to poor seeing (turbulent atmosphere)
On a more positive note, a 10" dob is a great starting scope for DSOs and the thing you may not realise is that many DSOs (btw by DSO I mean Deep Sky Objects such as nebula, open clusters, globular clusters and galaxies) are actually quite large. Mars this opposition only reached a maximum size of 15" which is really small. This chart,
http://www.nakedeyeplanets.com/mars-...ns.htm#oppdata shows the relative sizes of the planet for the next few apparitions. DSOs are quite large, Omega Centauri by comparison is 36' in diameter, effectively over 70x bigger, although the outer edges are fairly faint so you may not see it as large.
So do not despair! And with eyepieces my usual advice is get used to the ones you have and what works or doesn't work for you before spending money on more. And I wouldn't bother getting a plossl shorter than the 9mm you have for a couple of reasons. 1. They are harder to use, very tight eye relief and small exit pupil once down under 9mm and 2. Power or magnification is not always good. It also magnifies any poor seeing or movement of the scope and can be very tricky to get good focus.
Malcolm