I am same age. Your first pic is fine for sitting around the house but not so much for going anywhere you want to feel good.
I did however go out in skinny jeans (grey) with a long grey cardi today so I felt for you saying you're frumpy.
I'm a bit frumpy too but have recently retooled my wardrobe towards a hush like look. I don't necessarily spend a fortune. I have a lot of cuffed cotton trousers from gap in different colours. I wear them with clunky Chelsea boots I got very cheaply from asda. I have few cosy sweatshirts in animal print and camo. I'm going crazy for khaki and animal print at the moment.
Have you tried a big tesco extra? They have some nice things cheaply.
Get a pair of joggers preferably not actually flannel if you can find in a normal fabric
Try an animal print top or something a bit bold, maybe plain but not pastel or wishy washy?
Maybe try and find a pair of straight jeans you can roll up above your boots.
Buy some socks you aren't ashamed to see above your boots.
Get a chunky clunky pair of boots!
Get a pair of leggings and wear with a bolder but loose fitting sweat shirt dress. Or shirt dress?
John Lewis have some sweat shirts in at reasonable prices. They have a new basics range that could be worth trying for leggings and joggers. They had khaki joggers with a stripe down the side and a khaki sweatshirt with like zebra print on it. Could look really good with a pair of black Chelsea boots.
I like boots with a cuffed trouser as I think it's too cold in the winter for trainers.