Planets are very small objects. Getting a camera with a bigger sensor won't help you here. The 23MP of the Sony a6000 is already more than enough.
Make sure you're capturing them when they're at their highest point and when the seeing is at its best. I like to check meteoblue. When the "arc sec" value is low, below 1.0, then you should get great pictures. If it's above 1.5 then probably don't bother trying.
The lowest I've had was 0.60 and that night I was able to see details on Jupiter which I'd never been able to see before.
More aperture will get you better resolution, but first you might want to try a Barlow lens. A 5x Powermate will give a noticeable improvement. If that's too expensive then even a relatively cheap Orion Tri-mag 3x Barlow, for example, will help.
Another thing you can try is to get an astrocamera with a high framerate. With many astrocameras a reduced resolution (a mode known as "Region of interest") can help achieve a higher framerate. You'd be looking for something with USB3 here: the higher data rate is needed to record high framerate video.
The key with this is to try and capture those fractions of a second of clear seeing - the technique is known as "lucky imaging".
Also an atmospheric dispersion corrector can help reduce the fringes of colour on either side of the planets.
Finally ensure that your focusing is as good as it can be. An electronic focuser can help here, though they're not cheap.
Here are a couple of images I have lying around on this computer that I did two years ago. They're not great, being my first attempts at planetary imaging, but they're all that I have to hand:
These were taken through a 10" Dobsonian with an Altair 385C. Neither of those are the right tools for the job!
I recorded video, then used PIPP to extract the frames and centre and crop each one, then I used Registax's wavelet post-processing on Jupiter. It's over-processed. I was playing around to see if I could sharpen it up and I went too far.
With the Saturn image I just stacked it and didn't post-process. I was experimenting with different software at the time.
So to conclude, before getting a new telescope, try:
- a Barlow or Powermate (if you get a new telescope in future you can continue to use this)
- an astrocamera with high framerate and low resolution (if you do deep sky astrophotography in future you can use this as a guide camera)
- optionally, an atmospheric dispersion corrector
- possibly an electronic focuser
- and finally work on your post-processing skills: I use PIPP to centre and crop, AutoStakkert to stack, and Registax's linked wavelets to sharpen.
I'm not an expert by any means. Have a look at Cloudy Nights planetary imaging forum for more information from actual experts.