Thanks so much for your kind and understanding post, Helen - that is reassuring indeed!
Removal of 25+ nodes makes my 3 or 4 each side sound paltry in comparison .
Thanks so much for such a very helpful and comprehensive reply. I'm ordering both of the booklets you suggested and I've also read through/bookmarked for further perusal the 'Exercise and bad arm' thread.
I actually had SNB on both sides - perhaps if I'd known more about the lymphedema risk I'd have asked to have had it done on the left side only, as on the right the cancer they eventually found (via an MRI-guided biopsy) was very small in size and of the slowest growth rate ... But perhaps not, as at least I don't have to worry now about the possibility, however remote, of it having gone beyond the breast!
It's great to hear that nowadays you're using your arm as normal - it's that kind of anecdotal advice which makes all the difference.
Many thanks again, Chick!
Hope you are recovering well. Glad your nodes were clear. That is quite a challenge having a double mastectomy, both physically and emotionally. Hope the post operative arm exercises are going to plan. When you say you had SNB, was this just on one side?
From my own experience, there seems to be a lot of misunderstandings, myths and contradictions when it comes to this topic I am like you in that I had SNB so the risk is lessened. I use to worry about it when I first found out about it but I just use my arm as normal now and don't restrict on the weight bearing activities.
There is another recent thread regarding Lymphoedema in this section. It is under "Recovering From Treatment, Exercise And Bad Arm". I copied the current NICE Guidelines for that thread and have also replicated them below for your information.
There are two excellent booklets available free from Breast Cancer Care. Just go to the main site then click on the menu (the 4 bars), then click "Information And support" and then "publications" find them from the index or alternatively, just put BCC15 and BCC5 in the Search box on the right and booklet info for each should appear. You can download the booklets if you want. The full titles are Reducing The Risk Of Lymphoedema BCC15, and Living With Lymphoedema After Breast Cancer BCC5.
If it is any help, then below are NICE Guidelines (England) regarding the matter:
1.12 Complications of local treatment and menopausal symptoms
1.12.1 Inform people with breast cancer about the risk of developing lymphoedema, and give them relevant written information before treatment with surgery and radiotherapy. 
1.12.2 Give advice on how to prevent infection that may cause or exacerbate lymphoedema to people who have had treatment for breast cancer. [2009, amended 2018]
1.12.3 When informing people with breast cancer about the risk of developing lymphoedema, advise them that:
they do not need to restrict their physical activity
there is no consistent evidence of increased risk of lymphoedema associated with air travel, travel to hot countries, manicures, hot‑tub use or sports injuries
there is no consistent evidence of increased risk of lymphoedema associated with medical procedures (for example, blood tests, injections, intravenous medicines and blood pressure measurement) on the treated side, and the decision to perform medical procedures using the arm on the treated side should depend on clinical need and the possibility of alternatives. 
Mind you I have never had any one really discuss the risk with me or inform me of any dos and don'ts. I have raised it with some medical staff at times and they do not seem to know very much about it. I just do blood tests, blood pressure etc on the non surgical side/arm anyway irrespective of what it says above as it is no big deal for me to avoid the other side at the moment and why tempt fate!
Where people have had SNB or other, including radiotherapy to both sides, I have heard that they have used leg for BP, injections, bloods. I did have to have a cannula in my foot at one point when I was in hospital because my arms were so bruised and battered, so it can be done.
All the best Rose
Chick X 🐣
Two weeks ago I had a double mastectomy/sentinel node biopsy, and I am still feeling fortunate beyond belief that the lymph nodes turned out to be clear.
However, I'm now trying to get my head round what it means to live ongoing with the risk of lymphedema, particularly as I live on my own.
Does anyone have any advice, beyond the standard 'Don't carry heavy shopping bags/avoid cuts etc'? If I go away, for example, can I really not lift a smallish suitcase into the car? Are there recommended cases on wheels/shopping trolleys which would help me to cope?
I do understand that, in the first place, the risk is not so great as if I'd had to have more than the 3 lymph nodes removed on each side, and it's obviously going to be a bit of a case of 'suck it and see', but it would be great to have some advice on how to steer a middle course between carting round large heavy bags and being too neurotic to lift a finger!
Has anyone written a book about this perhaps?