if you seriously hurt something, please realise i might not be steering you right here. actual injuries are out of my scope. but with that said:

i think getting the form is a good place to start, but it doesn't have to be either/or. you can also do 'accessory' things to help yourself get acquainted with the muscles you're going to use. understand i'm not an expert, but i kind of struggle to 'feel' my core too so here are some of the things i try to do:

- if you've never tried doing planks, that is one heck of a fast track to that 'engage your abs' sensation. and if you've never done one before, prepare for very short endurance. i think my first plank lasted 20 seconds at the most, and the next day i discovered we have all these muscles between our ribs that i hadn't known about. they all hurt like hell.
- you could look up the valsalva manoeuvre and play with that as an exercise in its own right. breathing into the belly was something i had to consciously concentrate on and i'm still kind of left-handed at it.
- front squats actually help me with the core thing. you need to stay more upright, and you need to keep your chest up. so i do them almost just so i'll be remembering how to recruit those muscles and how it should feel when i do.
- goblet squats with a kettlebell are another one. i also just practice getting down into the bottom position with a kettlebell held in front of me, and then 'holding' myself there. when you hold the position, you have to breathe, and when you breathe in the position it's easier to figure out how to breathe consciously and make the right muscles work to do it.
- look around for info on various 'carry' moves. this is as simple as it gets - just walking around with a weight either in your hands [suitcase carry] or stacked on one shoulder [farmer carry]. it's simple but one or two ciruits of that are a hell of a core activator.

i also do dimel deadlifts (see google) as an accessory lift for hamstrings. in my case this is because i suck at squats, not deadlifts. but i'm effectively 'not squatting' at all because i still can't seem to do it without doing it wrong. be careful with the dimels though as they involve the 'hip hinge' movement and i can tell you that very subtle form differences can make my s.i. joint feel pretty crunchy on the next day.

as far as trainers go: gmpfhm. this is very personal choice, but i don't really regret holding out for a year and a half before i looked for one. i definitely did a lot of things wrong when i was on my own, but i don't think 'training' is for everyone. if you're like me, then there's no point in finding a trainer until you know enough to know how to find the kind of trainer who can actually help. and in my case, that took a patch of time where i defined my criteria in my own mind.

you're using good sources with thrall and rippetoe, i believe.

Has anyone else encountered the sexist form correctors? My gym is pretty segregated, women in the cardio area men in the weight lifting area. Any time I go into the weight area without my husband some random guy corrects my form. Today I started my first 5x5 workout. I watched the videos twice and practiced my form before going to the gym. While I was doing the barbell row, an old guy came up to me and was like "you don't want to do that exercise it will make your back too big. Stick to the squats." I can't imagine having the audacity to tell a stranger what part of their body they should workout. I could tell that he thought he was being nice so I just smiled and nodded telling him that I was following a specific workout, but I know that his assumption is that because I'm a woman I don't know what I'm doing and he has every right to correct me. It's 2016 in NYC and this is still happening?!?

nobody's done that to me, but i'm sure they would if i were 20 years younger. how freaking presumptuous.

So, he didn't want your back to get too "big", but he didn't mind if it was your booty. Typical, lol.