Cochem to Interlaken
 

I will be traveling with a friend from Cochem (Mosel) to Interlaken (SW) by Train. I know this is a rather long distance to cover in one day, so I am thinking perhaps we should break up the trip with a one night stopover somewhere along the way, either in Germany or Switzerland. Any suggestions that are easy to get to by rail without a lot of train changes?

Cochem to Koblenz - change to mainline trains to Mannheim and Basel, Switzerland, where many German trains on this route end.

Basel direct to Interlaken

Consider breaking your journey in Freibourg, in the Black Forest area - a real neat old town not seemingly destroyed in WW2 like so many German towns were.

For exact sample schedules go to the home page of www.budgeteuropetravel.com and click on the link "Best On-line All-Europe train timetable (or some such wording) and this brings you to the English schedule page of the fabulous www.bahn.de or German Railways pan-European train schedules with a From and To box and date and you'll get all the trains for that specific date - if your date is not loaded yet just put a dummy date in that is - train schedules rarely change that much and for planning purposes that is OK.
I reference this home page link because it also gives you some valuable tips for using www.bahn.de that may not be apparent at first encounter - the site if you know how to use it fully gives you a lot more than just train schedules.

Cochem - Interlaken can easily be done in an afternoon, for example: Cochem dp 14.58 - Interlaken ar 21.57, change at Koblenz and Mannheim.
If you want to stop over somewhere in the middle of the trip, check Strasbourg, Colmar, Freiburg im Breisgau. All depends on your interests.
My suggestion: Cochem dp 14.58 - Strasbourg ar 19.25, change at Saarbruecken. Sleep in the historic city center, do some visits (cathedral, etc.) the folowing morning and leave Strasbourg at 11.51 - Interlaken ar 15.28, change at Basel

well some folks who like to arrive earlier than 10pm in Interlaken - and you can of course leave any hour and do it in similar times - like leave at 9am and be in Interlaken by 5-6pm.