Unless you're willing to look at one of the aviation-specific portable GPS/mapping units (e.g. AvMap, Garmin, iFly), there's really very little option other than one of the tablet products on the market, and you'll have the same sunlight readability problem with all of them.

I'm not a huge fan of Apple products generally (written with an iPhone inches from my hand...), but there are more aviation apps available for the iPad than any other tablet. I'm sure Android tablets run a close second, and the Microsoft Surface products run a very distant third. I've owned a Surface (I'm typing this reply on it) for several years and I love it for general computer work, but it would make a poor EFB.

I use a 9.7" iPad Pro at work and it does the job fine. I've never had overheating problems in more than 10 years of aviation iPad use, but I work in an air conditioned flight deck. I've read that a mount with an integral fan can help prevent overheating in a GA airplane. Glare on the screen can be mitigated with a matte-finish screen protector film; I have one on my work iPad and it helps a lot.

You'll need some means of charging the device in the airplane, as a full-bright screen setting will murder the battery in very short order.

Regarding software, I can't offer much help. I've only used the apps my employer provides, and they're either ruinously expensive or not very applicable to VFR GA flying, or both.

WRT Joe's suggestion above, FltPlan Go appears to have an app for the iPhone, but not the iPad. You can run iPhone apps on an iPad, but you'll have to use a zoomed display mode and they won't make use of the whole screen. The Google Play Store does list a FltPlan Go app for Android tablets.