The size gap is perfect

Try these?
I think these probably have the biggest contrast between the seme and uke.
http://www.mangago.zone/read-manga/shitteru_yo/
http://www.mangago.zone/read-manga/shiba_kun_to_shepherd_san/
http://www.mangago.zone/read-manga/hard_x_heat_x_heart/
http://www.mangago.zone/read-manga/porno_superstar/
http://www.mangago.zone/read-manga/apron_yankee/
http://www.mangago.zone/read-manga/the_heart_of_red_cloak/
http://www.mangago.zone/read-manga/moonlight_howling/
http://www.mangago.zone/read-manga/hatsukoi_encounter/?pzJO
http://www.mangago.zone/read-manga/teddy_bear_no_wakarekata/

Here's some more if you read through the ones above/they don't really do it for you
honestly when I was going through what I was reading I had a hard time determining which were massively contrasting or if its just a big seme/average uke situation, so these are the ones that fell into the category of maybe closer to similar heights.

http://www.mangago.zone/read-manga/imperfect_pervert/
http://www.mangago.zone/read-manga/joukyuu_mazoku_no_otoshikata/
http://www.mangago.zone/read-manga/naruse_akira_to_ikkai_ya_retara_ore_wa_mou_shinde_mo_ii/
http://www.mangago.zone/read-manga/fukigen_na_kimi_to_kimagure_na_kiss/
http://www.mangago.zone/read-manga/neko_to_spica/
http://www.mangago.zone/read-manga/hinekure_chaser/
http://www.mangago.zone/read-manga/delivery_boy_debacle/
http://www.mangago.zone/read-manga/katekyo/
http://www.mangago.zone/read-manga/suki_nante_iwantoite/

Honestly it seems as though when there's a seme the size of a tree (in both ways :) ) the uke also happens to be a very large individual. Please try these and enjoy! I would love to hear ur opinions of all of these bl/manhwa, a lot of these are ones that I have enjoyed with the height diff playing a part. I feel like I've read a bl specifically about two childhood friends where the seme is stupid tall and the uke is short and has a height complex. I can't find it rn, but if I find it I'll get it to you!
Happy Reading!
Gigi ╮(￣▽￣)╭

ok here is the specific Manga I was talking about (ノ≧∇≦)ノ
http://www.mangago.zone/read-manga/chibi_demo_ii_yo/

I remember this one to be specifically cute with some possessive lover themes too!
If you want to find Manga like the ones above you might search by tags using the words 'height complex' or 'height gap' and you could probably find some good ones!

Sign

http://www.mangago.zone/read-manga/himitsu_ni_shiro_yo/

The Titans Bride

http://www.mangago.zone/home/mangalist/552975/

Titan's bride xD

Sugar Dog Life!!

http://www.mangago.zone/read-manga/sugar_dog_life/

Thank u all for the recommendations. Will check them out for sure

thank u so much for ur very detailed recommendations. Sorry for the late reply tho xoxo (=・ω・=)