I’d just suggest what you’ve probably already read - if you take it in tablet form, it’s better to start lower (like 10mg) and work your way up, as your body does progressively get more used to it.
Then I take it at bedtime, to sleep through the worst of the side effects, if you get them. If you get fatigue and brain fog the next day, which many of us do, it is good to schedule that day as quieter if possible. Drink bucketloads of water before you take it and in the next 24 hours - keep yourself well hydrated to minimise any headaches. And take 5mg of Folic acids (prescribed by your Rheumy) every day except the day you take the MTX.
Now days, I’m not terribly religious about any of the above. I started straight on 20mg and got noticeable side effects (including nausea, headache etc both that night and the next morning), but just muscled through them as MTX was my only option, and they weren’t completely debilitating. Within a few months the side effects of nausea etc were just that night, so I pretty much slept through them then had brain fatigue and fog the next day. Within a few years, I have no side effects, except a slightly better nights sleep.
Hope it is the boost your Costenyx needs