Well, maybe Taral V might be a nice place to start. The difficulty within
the flashpoints for the bosses ramps up nicely.
The first guy (with the 2 pet adds) is basically a joke, and the captain with his mini wannabe rancor is also quite doable.
The doc shouldn't pose too much of a problem (or can be skipped if he does), and then you're up against Lord Hasper & the droid.
Again, no enrage timers so you should be good.
Only the last boss has a hard enrage timer (I think it's 2 minutes) that puts you on the clock.
If you have some area damage and your dps is okay, you might also give Eselles a try, but the 2nd boss can be a gamebreaker for some, and without some kind of AoE damage you might not even get past the first boss.
If you're Jedi Sentinel heavy you could try Directive 7 - tons of droids in there, but there's a 400k in 4 (or is it 3?) minutes dps gating boss called bulwark in there
If you're going hard modes, expect bugs, bugs and bugs. For example in Taral V the research stations should spawn jungle creepers. They do, but on some, those creepers spawn at the flashpoint start and run to you from there, so you might miss them. If you're doing a boss fight while they arrive, things might get interesting
Also bosses might bug out on you. We've wasted 2 days on Mentor in D7 because he wouldn't get vulnerable after killing all 4 cores, or would start the fight with his laser, or his rockets or everything at once