Re:Low impact cardio (injuries)
It could be that you've tried doing too much too quickly. Have you had difficulty with joints before?
I've taken the past couple of months to slowly build the strength back in my knees so as to avoid injury.
With regards to buying a crosstrainer - to get the same sort of quality machine as you would in a gym you'd have to spend quite a lot of money, but if you can afford it and have the space then that's great. I don't know how tall or how heavy you are but you'll have to keep an eye out for a few features like length of stride, max user weight, resistance (get magnetic with the heaviest flywheel possible! as it it'll be 'smoother'), speed capability (how much it can handle if you go full pelt!), location of the flywheel, breaking system, power (does it need the mains outlet?), footplates, and finally - the warranties! It may be worth investing in a better quality one simply for the after-care service as getting it fixed can become expensive.
I think I covered the main features. Can't recommend anything for the rower but I'm sure if you have a search it might have already been covered in a past thread.
Best of luck!