The best way in economy is not the cheapest. It is IAH-JFK maybe 1000-1300. JFK-LHR maybe 0900-2100. LHR-FRA maybe 0800-1100. However, that would take 3 days of travel. The JFK-LHR part would be a daytime flight, not a red eye. Not tiring at all.

The next best thing is to try to adjust to German time while in the US. Not completely possible but try to go to bed at 7 pm for at least a week and get up at 3 am. 3 am is 10 am in Germany. If you can manage to get up at 2 am in Houston, that is 9 am in Germany. Then if you later get up at 8 am in Germany, that is only 1 hour of jet lag, 8 am vs. 9 am.