Hi Suzanne,
I am not a specialist in this area and just answering because no one else has yet.
Let's try and sort through your post.

1) Arthroscopy/ diagnosis: The only grading system I am aware of assesses the cartilage condition inside the knee. However, this is a 5-point score (0 - 4) and a 3.5 there pretty much means that you have next to no cartilage left, leaving the bone exposed. Not a pretty picture. Therefore, the doctors will recommend a TKJR. It is not up to Physios to comment on whether this is the best option, nor whether there are alternatives. There is different kinds of implants and not all limit kneeling. You should discuss this with a surgeon or your GP.

2) Appliance to regain strength: sorry, pretty much a 'no'. Strength gain is done with a specifically designed exercise programme. Frequency, duration and intensity depend on your condition. This needs to be assessed, e.g. by a Physio, and you will have to do the work.

3) Appliance to help you kneel down and get up discretely: not sure what you mean. Which leg are you wanting to kneel down on? Do you have problems with that now, both down and up again? And why? I do not know any machines that could do this.

4) Achilles tendon reflex: this reflex is not a functionally valuable reflex, i.e. it does not help with kneeling down or getting up.

It seems that your goal is to be able to kneel down and rise again independently. Is that correct?
This function is rather complex and involves a lot of strategies, which are impacted by single factors which could have impairments (what e.g. is the stregth of your quadriceps or calf muscles on either side? how about range of movement? any inflammation?) . In order to help you, we would first need to know what your problems is at impairment and strategy level. For this, I'd recommend that you get yourself assessed by a Physio specialising in Orthopaedics.

Hope this helps a little,
good luck,
Fyzzio