Your experiences are expected. The higher you push in terms of mag, the harder seeing will be regardless of the EP. On good nights you might push it up beyond a 9mm, but not on a regular basis.
I found the longer I was observing with my 10" dob, the less I looked at planets. So I would advise caution before jumping out and spending your budget on a top eyepiece that is less than 9mm in focal length. I went through the same as you and got a 4.8mm Nagler when I first got my dob. I was so excited to see the moon and planets that I wanted a large FOV (same as you) to not move the scope all the time and higher mag... I wish I hadn't none since i went on to enjoy globular clusters much more than the planets (but maybe that is just me!).
I was only 20 or so when I got that Nagler, so it broke my budget for a while. I was careful in making my next purchase and got a 32mm TV Plossl - best decision. Good quality. Low power suited what I ended up viewing (deep sky). Good price.
Food for thought!
