Mobility aid

Does anyone know of a mobility aid for a large dog that’s kind of like a scooter or tall skateboard where they can rest their torso on it but still use all their legs? My lab mix is 13.5 and has weakened back legs, but she can still walk. She loves going on the park paths and I was trying to find something that offers support so she can be steady, but still move all on her own. Thanks!