Have I recommended "Starting Strength" or "New Rules of Lifting" to you yet?
SS has some of the best instruction on the big basic compound exercises - much better than most internet resources and even most fitness instructors can or will provide. The program itself is primarily focused on maximal strength, but will produce muscle gains with appropriate nutrition. That said, I wouldn't recommend following the very brief nutritional recommendations in the book, which add up to about 5,000kcal/day :| Even if you never do the program, the technique instruction is priceless.
NROL (and NROL4W [NROL for Women]) is a good resource with a variety of exercise programs. It doesn't matter if you go for NROL, NROL4W, or both - the first thing you'll read in NROL4W is that women should be training the same way men train, so the programs should all amount to the same overall results.
You're already doing bodypump regularly. The best thing you can do to build muscle is to progressively increase your load. I think the normal recommendations in bodypump are to increase the weight every 6 weeks. Instead, until you get the courage to go out onto the gym floor (and then discover that it's really not so bad after all), focus on increasing weight as often as possible (without sacrificing form). I'd aim for an increase in weight every week if possible, even if it's only the smallest increase available.
Just to make a point on progression, if you have a look in my own journal on here, about a year ago I squatted 35kg. Once I was squatting 60kg+, it was getting hard. Initially I was aiming to increase weight - just by the smallest amount possible - every session. Above 60kg, I've stalled many times, had to reset the weight and work back up. I've had health issues and time out of the gym completely, setting me back further. As the weight's gotten heavier and heavier, I've had to slow down progress from day to day to aiming for only once a week, and not always getting there each week. Now, where you're currently at, you have so much more potential for improvement than I've got. Last I heard, you were squatting 12kg. I honestly think that if I were training you and we took you out of pump classes and got you on the gym floor, I could have you squatting 40-50kg by the end of this month just started, possibly more, just by adding the tiniest bit of weight onto the bar with every session.
It's the most basic of muscle building techniques. Lift a weight. Eat. Recover. Lift slightly more weight. Repeat. It's not super fun or interesting, it's not glossy or cutting edge. It's boring and simple. But it works.
So here goes...