I would think about keeping the Iphone (for basic calls/texts etc) & getting a fairly nice 10" tablet for other uses. I'm not an expert, but don't the better tablets often have an advantage of lighter weight, more battery life & faster processors than the cheaper ones? A laptop has the advantage of the separate keyboard but that's extra weight & folks seem to manage without it in most cases. Also, light-weight laptops seem to be a bit pricey.
Those portable Bluetooth keyboards are pretty cheap & light but I don't know if I would bother, another thing to charge. & yes, the whole charging bit is a problem. A big power bank adds some weight but adds flexibility, perhaps one would only need to charge phone/tablet/power bank once a week?