I am always for the simplest and least painful solution. The one that can stick.
If you are only looking towards your arms, I would recommend simple pushups.
Include these in your morning routine before your shower for example.
Do not try hard, start with as few as you wish. If one is too much, try on your knees.
But do these every morning. Just doing it daily or so and you will see results within weeks.
Most of time, people stop or fail because trying too much too fast.
Let us know what you decide to do and how it goes !
ps : I recommend this to a friend and she is seeing results after only a couple of weeks