What kind of issues are you having right now with the bar end shifters? Trouble riding one handed?

My guess is that you are death gripping the bars when you try to go one-handed. Loosen up. Way up. I know this sounds counterintuitive, but you will be a better bike handler if you keep a very light hold of your bars. You'll aslo be a lot more comfortable.

For now, put the bike on your trainer and practice shifting and getting your water bottle out and into its cage without looking down. Stay relaxed as you do. Then get back on the road and try it.

Keep telling yourself that you can do this; it just takes practice.