well done getting the diet sorted: this is the most important part when you'r trying to lose weight/get in shape. Aiming to lose 1-2lbs a week is sensible, and suggests that you're not going to crash diet or burn out, so well done for that, too. Wise bird!
HIIT, in my opinion, is crap UNLESS you're totally healthy and in your 20's. With a bum knee and a bad back, I'd say NO!!!!
Zumba is great fun, and is a proper work out, but one zumba class a week won't do you any real good, in terms of fitness.
If you enjoy it: great, add it to your schedule, but I wouldn't rely on it.
Same with the gym: unless you've got lots of free time and money and can go to the gym every single day, and work out for around an hour each time, and factor in travel, and factor in getting changed and showered before and after, then you won't see any real body changes. Most people over-estimate the work they do in the gym, they don't have the correct form to do the exercises, and there's lots of idiots, usually men, gegging in to tell you what to do and most of them are clueless...
Pilates and yoga: the same. Pretty useless, fitness-wise. Great as 'add-ons', but yoga won't help you lose weight, and neither will pilates. These classes are great for stretching, and toning, but... a bit too 'posho' and 'exclusive' for my liking!
Instead of HIIT (high impact and intensity), opt for LISS (low impact steady state). The best LISS walkout is ... walking. It's free, and easy, and all you need are a pair of trainers and a cheap waterproof coat. I'd recommend when starting out you do 30 minutes a day, every day, but (maybe) have Sundays off.
You need to walk at a fast enough pace so that if you was holding a conversation, you'd be breathless.
Once you've established that routine, say, after 30 days, then you can make it harder by adding wrist weights or carrying hand weights -- 2/3lbs is enough. Amazon, ebay, argos: they'll cost you around £5-10.
(I carry hand weights, 3lb each, and they double up as self defence batons!) Swing your arms when you're walking, imagine you're skiing and the hand weights are ski poles: that range of motion. This helps to tone up your arms and upper body, too.
You can also later, add ankle weights: again, 2/3lb one are best when starting out. Roughly the same price, too. This will strengthen and tone your legs and shouldn't damage your knee, either.
You can also, later, fill a rucksack with water bottles/tin cans/free weight plates) to increase your load: This will help to strengthen your core and your back, too.
All of this added weight makes your body work harder. Don't do it all at once though, or you'll hate it!
other tips?
Don't use the same route, each time: aim to walk in a different route most days. Don't listen to music, unless you're listening to EDM at around 220 BPM, as you'll automatically start walking to the beat, and you won't be getting the benefits of the pace.
don't be tempted to run, or jog: it's crap for your knees and back, and totally not necessary.
re: strengthening your pelvic floor: there's a yoga move called 'the modified bridge'. You lie on your back, with your knees up and feet on the floor, and you lift your hips off the floor while keeping shoulders and feet on the floor.
Do this move while clenching your inner vag. If you're not sure how to 'internally clench', then you have to have a feel and see if you're using the right muscles. Once you know which bits to be squeezing, imagine drawing your bits in, but incrementally, 1,2,3,4,5, with 5 being the tightest squeeze. Then, hold that squeeze for five seconds, and try to let go of that squeeze incrementally, too. Repeat this five times. Do this daily. If you can't manage the bridge, just do the squeezes. This is the easiest way to tone those internal muscles.
go girl, you got this! x