There are socks you can buy which are specifically designed to wear to bed after you lotion the hell out of your feet. A few nights of that and your feet will be crazy soft. Softer feet = more ticklish.
On that note, any time I went for a long hike (like an all day hike, 7 miles or more, and especially backpacking trips) any girl I've dated had waaaaaayyyy more ticklish feet. So... sore feet also = more ticklish. One indulged me by wearing nylons in her boots/pants and it was pretty fucking epic.
Also don't just assume that it is you. It could be that your boyfriend needs to learn how to tickle you better/fogure out what makes you tick. Usually it is a 2 way street.
Using silicone based lube like Uberlube works wonders on the bottoms of feet and in between the toes. That coupled with running pipe cleaners between toes works crazy well. There is a specific type of pipe cleaner which has little plastic pieces jutting out of them within the normal velvet like material.
Finally as some have noted here, certain drugs can enhance ticklishness as well. A strong Sativa weed strain works really well. Cocaine has also worked really well for me in the past and makes the overall experience 100x more intense for both myself as a ler and any women I've done it with as a lee. But I haven't done that shit in years. It's a terrible fucking drug. I had my fun, but it is really addictive and dangerous and I am happy to say that even though I'd like to do it again, I haven't in a few years and my desire not to is stronger than my desire to. The only way it's gonna stay that way is by not doing it again. Also Molly/MDMA works really well too but it is more of like a playful tickle intensity and not the usual "tickle torture" intensity.
And on a final note, while it's awesome you want to find ways to be more ticklish for your bf and is really sweet of you, don't feel as though you aren't enough or that there is something wrong with you. Or let him make you feel that way. Ever. Whatever that's worth to you.