Recommended planet pack for 1.4?

[Klapaucius]

At some point, I plan to give the Galileo game a go, but that will require doing a lot of backup beforehand.   For the moment, I'd just like to add some planets.  What planet pack would you recommend that expands the Kerbol system without changing the planets that are already there or altering the stock game physics that works in the latest versions of KSP?

[Lisias]

You will find that you must stick with 1.4.3 until further notice, as 1.4.4 is internally broken for Kopernicus (a mod that allows planet packs), something that is expected to be fixed at 1.4.5.

That said, I think  you will like this thread:

 

Edited July 24, 2018 by Lisias

[OhioBob]

Outer Planets Mod is a good choice.

 

[Snark]

Moving to Add-on Discussions.

 

22 hours ago, Klapaucius said:

What planet pack would you recommend that expands the Kerbol system without changing the planets that are already there or altering the stock game physics that works in the latest versions of KSP?

If you want to leave the stock system alone, my favorite go-to choice would be Outer Planets (as @OhioBob links to, above).

What it does is to add Kerbalized versions of our own outer planets to the stock game.  We've already got Moho (Mercury), Eve (Venus), Kerbin (Earth), Duna (Mars), Dres (Ceres), Jool (Jupiter), and Eeloo (Pluto).

This mod adds Sarnus (Saturn), Urlum (Uranus), Neidon (Neptune), and Plock (Pluto), with appropriate retinues of moons for each (e.g. Sarnus has one moon that's a Titan analog, etc.)

It's masterfully done, the artwork is both beautiful and very "stockalike" so it fits very well with the stock system.

It doesn't quite leave the stock system untouched (it moves Eeloo to become a moon of Sarnus), but it's pretty close.

 

Other than OPM, my favorite planet packs are Galileo's Planet Pack and New Horizons, but both of those completely rejigger the solar system and therefore don't quite match what you've asked for, here.