First and foremost, some hyaluronic acid as hair serum worked for me.
Overall I have found the following products and techniques helpful though:
Olaplex 0 and 3 every few weeks.
Shampoo Shampoo and conditioner containing hyaluronic acid (Urtekram Nordic Berries).
CWC (condition-wash-condition) so wet hair, apply conditioner to lengths but not roots, then lather shampoo on hands before applying to hair. Rinse and then condition. I use butterfly clips to keep my hair up for 15-30 minutes with the conditioner on whilst I soak in the bath and read for a bit. Then rinse.
Every few weeks I use Christophe Robin Prickly Pear Treatment instead of my usual conditioner as the final stage. As @RhymesWithHaliborange says it is expensive but oh my god it is good.
After washing, spray on on leave in conditioner with hyaluronic acid in it (again Urtekram Nordic berries works for me). Then some Garden of Wisdom hyaluronic acid distributed through my hair and massaged into my scalp. Another quick spritz of the leave-in conditioner. Then I seal the ends with hair oil (I like inlight hair elixir) and rake through some Olaplex no 9 serum all over.
Rarely use heat, although I do blow dry on cool sometimes. I’ve also been known to stick on a fan heater and sit close to it, but not too close, to speed up drying.
Sounds a lot but I have to do a lot less to make my hair look good between washes, and I now only need to wash it 1-2 a week.