It sounds like your defensive game needs work. If you are facing a tough shot, it *may* be the case that a safety is the best shot, but this is highly dependent on the odds of you properly executing the safe. I play as a pretty strong 9. I just played a match against a good 4, and I won 75-3. I played 2 safes. They were both reasonably effective. 2 safes for me, particularly against a lower player, is very low. My point is that I simply felt the odds at each point favored the shot. I was playing well and really didn't face too many tough shots.
You say "messing around...with defensive shots". Does this mean you were trying things out? Why did you play safe? If the answer is something other than "because I felt my odds of executing the safe were better than my odds of executing the shot", then you might want to examine why you were playing safe. If you were trying to learn or practice something, maybe your match isn't the right time for that? Keep in mind that if you have doubts about a shot, you could probably use some practice on your shot making. However, doubts on a shot does not automatically mean that the safe is the right answer. I have to ask, if your safes didn't go too well, then didn't you have some doubt on your safes? If you have doubt both ways, go for the shot. To me it sounds like your best bet is to practice your cueball control, so that you can develop better safes that you are more consistent at executing.
Also, when I hear people talk about "getting in a rhythm"...this immediately makes me thing some work on the mental game is in order. If you can't get up for each shot that is presented to you, safe, hard shot, easy shot, whatever...then I think you need to evaluate your mental approach and maybe your shooting routine. Sometimes, you just never come to the table with easy stuff. You have to come through in those moments just as much as you do when running a cosmo out. To depend on a "rhythm" is to put yourself at a huge disadvantage in matches like that. If a rhythm comes, it comes. Ride it. But I disagree with the idea of "making a rhythm happen". Just play each shot the best way. Look at it as a unique test, put your attention into *this* shot, and nevermind what happens before or after.
So...my advice is practice cueball control, particularly with regard to playing safe, and practice the mindset of coming to the table and taking each shot as a single thing, unattached to the rest of the match, and just focus on doing *that one shot* the best you can.
Hope this helps!
KMRUNOUT