Wheelchair, cart, when? Features?
At the end of crate rest, many dogs are recovering to the degree that money is better spent on physical therapy to help them learn to walk again. If a wheelchair is needed while waiting on more nerve repair, then look for the specific features an IVDD dog needs.
Top priority is to let the disc heal completely by finishing 6 weeks post-op or 8 weeks conservative crate rest.
At the end of crate rest, you and your vet can better assess if a wheelchair is needed.
Keep in mind a cart is not for all day use, but rather a couple of hours at a time.
A paralyzed dog will use a cart everyday, it is better to save up for the best cart you can afford, than to purchase one that is ill fitting and inconvenient to get the dog in and out of.
A professionally made cart is likely to be much better than a homemade cart in regard to pressure points, balance & stability. Be careful where the yoke/ harness sits on your dog, you do not want to cause pain or further injury to an IVDD dog. Check with your vet or other professional.
Features to look for in a cart: https://dodgerslist.com/2020/06/06/wheelchairs/