All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
As far as we know, it is difficult to use the hoverboard and maintain balance on it except with effort. It is hard for the woman in sound health to use it, let alone a woman in your condition who suffers pain in the heels and knees.
In general, it is permissible to perform Tawaaf while riding for a valid excuse, and this Tawaaf is valid according to the agreement of scholars. Ibn Qudamah wrote:
“We do not know of any disagreement among the scholars regarding the validity of the Tawaaf while riding if the pilgrim has a valid excuse. Ibn ‘Abbaas said, ‘The Prophet, sallallaahu ‘alayhi wa sallam, performed Tawaaf in the Farewell Hajj on a camel and touched the corner (Black Stone) with a crooked stick.’ Umm Salamah said, ‘I complained to the Messenger of Allah, sallallaahu ‘alayhi wa sallam, of my ailment, whereupon he said, ‘Perform Tawaaf beyond the people (not close to the Ka'bah) while riding.” [Al-Bukhaari and Muslim] Jaabir said, ‘The Prophet, sallallaahu ‘alayhi wa sallam, performed Tawaaf around the House (the Ka’bah) and made Sa‘y between Safa and Marwah on his Camel so that the people could see him and ask him questions (about Hajj) for the people were crowding around him.’”
If you cannot afford the electric wheelchair, you can look for other alternatives, like the regular wheelchair, for instance.
Allah knows best.