I am currently 18 weeks post relaxer and I still do not really have a desire to relax my hair. Every time I stretch it seems to get easier and easier to go a few weeks longer. This is the longest I have ever stretched my relaxer to date. I really think that is the best way to begin stretching, start out by exceeding your normal time length by a week or two. Then the next time your due for a relaxer extend by an additional week or two, if you do that you will be on your own 17+ week stretch sooner than you think.
*Please remember that stretching relaxers is not for everyone and if you notice breakage as a result of stretching consider ending your stretch because something is not working for you. Just make sure it's really breakage as opposed to shedding, your shed hairs will have a white bulb on the tip, curly hair, then straight hair towards the end. If shedding bothers you try a Garlic shampoo or treatment and that should help.
Stretching your relaxers has many benefits, take it from me...I used to relax every 4-6 weeks, remember? That was long before my healthy hair care journey and before I had a healthy hair care regimen. Your wallet will thank you and so will your hair, because at the end of the day relaxers can be costly and the shorter your stretch the greater chance you have for overlapping relaxer on previously relaxed hair. Now that I relax less frequently I have seen a change in my hair as far as thickness goes.
While stretching it is important to keep your new growth well moisturized, this will help it stay soft. I use a spray moisturizer daily on the new growth and my hair loves me for it, I follow with some coconut oil. Also co-washes are a must and remember your shower comb! I also step up my deep conditioning regimen to twice (maybe even 3 times a week) during stretches. As for hairstyles during stretches, I end up wearing buns on an almost daily basis when I'm stretching just because it's easier and it keeps my ends protected. If you have to wear your hair straight for some reason, invest in a good flat iron so you can get those roots straight. Otherwise, try braid-outs, twist-outs, or roller-sets to switch up your looks.
Happy Relaxer Stretching!