Im not currently using one, but one i absolutely loved is called Target Specifics Pilates Its kinda old but man does it burn so good!! I used this daily before i got pregnant with my first and before we could afford a gym membership and personal trainer. It had awesome reviews back then and really kicked my ass. I pull it out every now and then still.
And, bonus, its only two bucks right now!! Pretty sure i paid 20 bucks for mine (2 or 3 times at that because i lost it once and broke it another time during a move) back in the day!
No advice, but I'm also 6 months PP and so frustrated with my feet!! Solidarity! I recently bought some extra arch support pads (these) and they seem to maybe be helping? I've been wearing them full-time unless I've been sleeping/showering and my feet feel better during the day. The mornings are still a little rough, though I think I may be seeing some slight improvement? I have no idea. I'm happy enough that I'll continue wearing them for the next several weeks and see if they fix whatever this is. It's horrible. I'm sorry that you're also suffering!
This is the protein powder I use as an additive: Ispoure Whey Protein. They have a 20% off coupon right now actually!