Or connect with the Assistance Dog Association, as they train smaller dogs as well that might just not have passed the final examination, but would make great and thoroughly tested family dogs.
https://assistancedogsinternational.org/
If you have a local animal shelter, you could connect and start walking some of the dogs (breeds) that might meet your requirements and by doing so, get more insight.
Yes, really. Watch some videos of professional dog groomers and you will find them talking quite freely about these doodle mutts and the mostly much underestimated grooming necessities/problems.
For starters...
Keep in mind that they need intense grooming (especially ears, butt, underside of paws between the toe pads) or else will get matted within a few days, ear infections, anal gland infections etc.
How about this one: https://duckduckgo.com/?t=ffab&q=basset+fauve+de+bretagne&iax=images&ia=images
ETA: Basset Griffon Vendeen:
https://duckduckgo.com/?q=basset+griffon+vendeen&t=ffab&iax=images&ia=images