The First Jhana is just sustained thought and attention on the object, with some sukkha (pleasure, bliss), and some piiti (rapture, ecstacy) which are
"First dhyāna: the first dhyana can be entered when one is secluded from sensuality and unskillful qualities, due to withdrawal and right effort. There is pīti ("rapture") and non-sensual sukha ("pleasure") as the result of seclusion, while vitarka-vicara ("discursive thought") continues" https://en.wikipedia.org/wiki/Dhy%C4%81na_in_Buddhism
"you will be overcome with rapture, euphoria, ecstasy, delight. These are all English words that are used to translate the Pali word piti. Perhaps the best English word for piti is “glee.” Piti is a primarily physical sensation that sweeps you powerfully into an altered state. But piti is not solely physical; as the suttas say, “On account of the presence of piti, there is mental exhilaration.” In addition to the physical energy and mental exhilaration, the piti will be accompanied by an emotional sensation of joy and happiness. The Pali word for this joy/happiness is sukha, the opposite of dukkha (pain, suffering). And if you can remain undistractedly focused on this experience of piti and sukha, that is the first jhana." Leigh Brasington - https://www.lionsroar.com/entering-the-jhanas/
It must be possible to experience these during sitting, standing, lying down, and walking, because they are standard positions for meditation. Eating is also used for meditation so that also. Conversing activates the discrimination mind, rather than the mind moving towards equanimity, so it will diminish the effect of the First Jhana. It is excellent to stabilize samadhi by doing these things, whilst in jhana, but preferably with Noble Silence.
"Huisi taught two different forms of the lotus samadhi. The "practice devoid of characteristics", or the practice of ease and bliss, is based on the fourteenth chapter of the Lotus Sutra. Huisi explains, "While in the very midst of phenomena [the practitioner discerns that] mental characteristics are quiescent and extinguished and ultimately do not arise. (...) He is constantly immersed in all the profound and wonderful dhyana absorptions because in all activities - walking, standing, sitting, lying down, eating or speaking - his mind is always settled [in samadhi]." https://en.wikipedia.org/wiki/Nanyue_Huisi