I am amazed by how you managed to make your garden look so mature in only six years! It's great. I must admit I am a little envious - I used to spend every spare minute in the garden, but having been unable to walk for some years, our garden grew into a wilderness.
Last year I decided to take drastic action. With my husband's help (he hates
gardening), I managed to chop down and dig up everything (except for half a dozen trees) in the back garden. It took the whole summer! We had to hire two large skips to get rid of tree trunks, roots, old pond liners, and rocks from the two rock gardens that had taken up a large part of the 40' x 40' space. After that, we put down a weed suppressing membrane on all of the borders, and covered it with chipped bark.
Our final act was to put a couple of dozen containers around the borders. Never having grown plants in containers before, it was all a bit hit and miss, so I put in a fairly large variety. Quite surprised that all but two managed to survive our harsh winter and cold spring. The lawn is still in pretty poor condition - dogs, compaction on clay soil, and general neglect, have meant that the grass is a bit sparse - but we couldn't manage to do much to it last year - and for health reasons, I haven't been out there much this year. But next year ....
I manage to get round on a wheeled garden seat, or with a walker/rollator - a bit comical at times, but ... I'll try and post some photos at some point if you're interested. Meantime, please do tell more about your garden - I love to read it and see photos.