Persulphate bleach is always damaging, more or less depending how many shades you lift, the initial health of your hair, whether it is fine or coarse and other factors.
If you have old damage you'd be best to grow this out before bleaching: hair is dead so can be made to feel and look better within a few weeks but permanent repairs are impossible, your hair will not be healthier in such a short space of time.
Proven beneficial ingredients for damaged hair include coconut oil, hydrolysed protein, ceramides, 18-MEA and panthenol. Both coconut oil and hydrolysed protein can reduce bleach damage if used as a pre-treatment.
Straightening can cause irreparable damage in just one session, be sure to use a low heat, only ever flat iron bone dry hair, use proven protective ingredients such as hydrolysed protein, glycerin, propylene glycol and certain polyquats.
2a-2c, medium texture, porous/ colour treated. Three years CG, growing out mechanical and chemical damage = breakage and very high porosity. Past armpit length heading for waist.
CO-wash: Inecto coconut
Treatments: Komaza Matani, coconut oil, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss ultimate volume, Inecto argan
Styler: Umberto Giannini jelly, Boots Essentials gel
Experimenting with: going back to basics